Happy to have been able to assist.  All USB controllers which have more than one downstream port have a 'root hub' and you "sub-hub" may well have been a poor performer.  Regardless, nice to know that all is now well.

Should you have any additional questions, please feel free to forward them as they arise.

Kevin Halverson
CTO
High Resolution Technologies, LLC

    From: <me>
    To: Kevin Halverson <kevin@hirestech.com>
    Sent: Thursday, May 9, 2013 6:28 PM
    Subject: Re: HiResTech.com Contact

    Using USBDeview, a similar utility to USBView, but with the ability to remove unused devices, I cleaned out over 60 unused device registrations and verified it was sipping the allotted 250mW without any hickups or error, very nice indeed.

    Perhaps the issue was that it was technically a sub-hub.  The USB 3.0 controller on my motherboard was a design afterthought and is just a hardwired controller/set of ports, thus it is registered as a hub, and my actual hub shows up as a sub-hub.

    In any event, in the 20 or so minutes between this email and the last, I haven't heard a single imperfection, it's aural bliss ;)

    You guys are truly awesome, first-class products and service that doesn't cost an arm and a leg!  I'll be sure to give you a shoutout on /r/headphones.

    Thanks again,

    <me>
    On 5/9/2013 9:23 PM, Kevin Halverson wrote:
>     I suspect that this was a case of a poorly performing USB subsystem and if you were to download and run a copy of USBView.exe from the Support page of our website, I suspect that you may have located a different controller and hence different root hub.
>
>     Should you have any additional questions, please feel free to forward them as they arise.
>
>     Kevin Halverson
>     CTO
>     High Resolution Technologies, LLC
>
>         From: <me>
>         To: Kevin Halverson mailto:kevin@hirestech.com
>         Sent: Thursday, May 9, 2013 6:00 PM
>         Subject: Re: HiResTech.com Contact
>
>         It seems, on first impression at least, that moving over to the on-board rear output has resolved the issue.  I'll "reopen" these emails again if that is not the case, but it appears my hub doesn't mesh well with the streamer.  Having it on the hub with the sleep/parking feature disabled did nothing, but I haven't heard anything yet on the rear output, both with sine, square, and sawtooth waves in my audio editor sweeping at -0.1dB from 20-20k and with music.  Thanks for the help, you can consider this resolved, at least for now...
>
>         -<me>
>
>         On 5/9/2013 8:46 PM, Kevin Halverson wrote:
>>         This of course presumes that it is a simple overload that is occurring.  A full scale sine signal would be a good test.  If you can't generate one, let me know and I will do so for you.
>>
>>         My other line of thinking was that if this is a poorly behaving USB controller, then yes, adding a USB 2.0 dedicated controller might be useful.
>>
>>         You may want to consider the microStreamer rather than the Music Streamer II for your application as you would avoid many of the suspected issues.
>>         Kevin Halverson
>>         CTO
>>         High Resolution Technologies, LLC
>>
>>             From: <me>
>>             To: Kevin Halverson mailto:kevin@hirestech.com
>>             Sent: Thursday, May 9, 2013 5:38 PM
>>             Subject: Re: HiResTech.com Contact
>>
>>             Perhaps it's actually clipping or something, but some additional details:
>>
>>             * it seems to be partially linked to what is being played back - well mastered tracks (ie: no clipping) show less click/pop/dropout than poorly mastered ones, and it almost seems to favor certain tracks.  That's probably all in my head though.
>>
>>             * Detaching the mic from the hub changes nothing.
>>
>>             * The hub has its own AC adapter and is not just a hub that carries 500mW over the USB cable and powers everything off that.
>>
>>             * My settings are already high power/high performance, but the "allow controller to sleep/park usb devices to save power" option was on, I've disabled that and will report back after a restart.  I'll try running it straight off the motherboard USB out as well.
>>
>>             * It could be dynamic range clipping, but I doubt it.  I run my digital output at 20/100 ticks on windows, 44.1k/24bits.  In theory, I should be padded against that, and very quiet classical tracks don't show nearly as many artifacts.  The reason I do that is because the combination of the MSII's 2.25V output, and the tremendous power of the Objective 2 feeding my very sensitive IEMs (17 ohm/117dB sensitivity) means I can't have digital volume output anywhere *near* even 50%, or I won't even get past the point on the O2 knob where channel imbalance is a nonissue.  Even at 20/100, I don't even make it to the 9 oclock position, at which point I'm even a little louder than I would wish to be.  20/100 or 10/100 show equal artifact (that's what they are, I believe) amounts. It's not loudness war / brickwalling style clipping just showing up, my very high quality Cowon Z2 has never clicked or popped on me, and while it isn't as good as my O2/MSII stack, it's no slouch.
>>
>>             Re: your other email,
>>
>>             My motherboard has the PCI-E x16 slot filled with my GPU, an additional slot filled with my wireless network adapter, and the other two are fairly inaccessible, due to the bulk of my GPU.  I could probably move the wireless adapter over a slot and squeeze another device in, if that's what you have in mind, but it would be tight.
>>
>>             Anyway, I've disabled the parking option in the power menu and will be restarting my computer now.  I'll try a main port on the rear of the machine as well and report back in about an hour or so.
>>
>>             Thanks,
>>
>>             <me>
>>             On 5/9/2013 7:29 PM, Kevin Halverson wrote:
>>>             The issues of power when one considers a USB controller is not in the traditional sense, it is computational power that is the limiting factor.  I would recommend a number of things that can improve this computer's performance.
>>>
>>>             1) Use a dedicated self (not bus) powered USB 2.0 hub between the host (computer) and the device (Streamer in this case) making certain that the only device attached to the hub is the Streamer.
>>>             2) Disconnect the microphone from the host (at least for testing).
>>>             3) Set the host's power management to "High power" (this will require a restart).
>>>             4) Consider running an optimizer such as fidelizer (http://www.windowsxlive.net/fidelizer/)
>>>             5) Setup the host according to the Vista / Windows 7 instructions as shown on the Support page of the HRT website.
>>>             6) Test using Windows Media Player.
>>>
>>>             Please report back your findings.
>>>
>>>             Kevin Halverson
>>>             CTO
>>>             High Resolution Technologies, LLC
>>>
>>>                 From: <me>
>>>                 To: Kevin Halverson mailto:kevin@hirestech.com
>>>                 Sent: Thursday, May 9, 2013 12:32 PM
>>>                 Subject: Re: HiResTech.com Contact
>>>
>>>                 I'm running Windows 7 x64, using the Zune software, although I could force myself to suffer through iTunes if that would work better.  Foobar2k works too, but I don't want to go through the hassle of making it look the way I want and only getting 70% of the way there.
>>>
>>>                 Fully custom built desktop PC, all the rest of the details below,
>>>
>>>                 PC Components:
>>>                 -AMD phenom 1100T x6 - former flagship processor
>>>                 -AMD 6950 2GB GPU - near top-of-the-line graphics card
>>>                 -Asus M4A87T motherboard + USB 3.0 controller
>>>                 -1TB Seagate Barracuda HDD
>>>                 -8GB of RAM (way more than necessary, I'm not running into RAM issues)
>>>                 ----
>>>
>>>                 USBs, desktop rear has 4x USB 3.0 occupied as follows:
>>>
>>>                 -Keyboard
>>>                 -Mouse
>>>                 - Backup external HDD (2TB)
>>>                 - powered USB 3.0 hub
>>>                 ---AKG Perception 120 mic
>>>                 ---Cowon Z2 USB/charger cable (USB mini type b, only in use ~33% of the time)
>>>                 ---Printer (rarely in use)
>>>                 ---MSII
>>>                 -----
>>>
>>>                 It's entirely possible it's a data bandwidth issue on the hub, or hickups in its controller, it's just a $20 generic "protronix" thing, but it's well made and has tight fit 'n finish, I doubt it's running into bandwidth issues, the mic sends data constantly but isn't high bandwidth, and the other two ports aren't actually doing anything most of the time.   Should I try moving the MSII to an actual rear port so it's being fed directly?  The mobo is a 2011/2012 product, so it should be able to push 250mW out all the rear ports adequately...
>>>
>>>                 Thanks,
>>>
>>>                 <me>
>>>
>>>                 On 5/9/2013 12:02 PM, Kevin Halverson wrote:
>>>>                 What you are describing is a computer that is marginal in terms of its USB performance.  The 'fix' is to improve the computer's abilities so that it doesn't send bad data.
>>>>
>>>>                 A few questions:
>>>>
>>>>                 1) What OS are you running?
>>>>                 2) What media player are you running?
>>>>                 3) Is this a desktop or portable class machine?
>>>>                 4) Please list any and all USB devices attached.
>>>>
>>>>                 Kevin Halverson
>>>>                 CTO
>>>>                 High Resolution Technologies, LLC
>>>>
>>>>                     From: <me>
>>>>                     To: sales@hirestech.com
>>>>                     Sent: Wednesday, May 8, 2013 6:33 PM
>>>>                     Subject: HiResTech.com Contact
>>>>
>>>>                     Every once in a while, I hear a sharp click or a pop (or quick drop and reacquisition of signal broadcast) out of my MS II, possibly once or twice an hour(ish) in frequency, but it's irregular.
>>>>
>>>>                     Is it timing issue with the asynchronous nature of the DAC?  Could my analog cable be picking up interference (I doubt it)?  Can it be fixed with a firmware update?  It shouldn't be powering issues, it's plugged into a simple 4-port powered hub, either.  Checking the firmware, it's on Revision 2.  Should I use the Upstream utility to push Rev2_v3 to it?