(^.*)(?<=()(.*?)(,)(.*)(?=))(.*$)

room_ass=01:macro_id=01: name=Left, pgm_audio=0, usb=0, list=(1*,3,5,7,),
room_ass=01:macro_id=02: name=Right, pgm_audio=1, usb=1, list=(2*,4,6,8,),
room_ass=01:macro_id=03: name=All, pgm_audio=1, list=(1,2*,3,4,5,6,7,8,),

room_ass=01: macro_id=01: name=Left, pgm_audio=0, usb=0, list=(1*.3.5.7.),
room_ass=01: macro_id=02: name=Right, pgm_audio=1, usb=1, list=(2*.4.6.8.),
room_ass=01: macro_id=03: name=All, pgm_audio=1, list=(1.2*.3.4.5.6.7.8.),

(^.*)(?<=()([^,]*)([,|d|*]3.*)(?=))(.*$)
                   (          ^  )

room_ass=01:macro_id=01: name=Left, pgm_audio=0, usb=0, list=(1*,3,5,7,),
                                                      iter 1-|  ^      |
                                                           2-|    ^    |
                                                           3-|      ^  |
                                                           4-|        ^|

((?:(?:[^,)]+),)*?(?:[^,)]+)K,