ffmpeg demux of Dolby Surround in .ac3

$ ffprobe -v error -show_entries stream=channels,channel_layout -of default=nw=1 test.ac3
channels=2
channel_layout=stereo

$ ffmpeg -i test.ac3 -filter_complex "channelsplit=channel_layout=5.1[FL][FR][FC][LFE][BL][BR]" -map "[FL]" front_left.wav -map "[FR]" front_right.wav -map "[FC]" front_center.wav -map "[LFE]" low_frequency_effects.wav -map "[BL]" back_left.wav -map "[BR]" back_right.wav
ffmpeg version 4.3.1 Copyright (c) 2000-2020 the FFmpeg developers
  built with Apple clang version 12.0.0 (clang-1200.0.32.29)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.3.1_9 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libdav1d --enable-libmp3lame --enable-libopus --enable-librav1e --enable-librubberband --enable-libsnappy --enable-libsrt --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxml2 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-libzmq --enable-libzimg --disable-libjack --disable-indev=jack --enable-videotoolbox
  libavutil      56. 51.100 / 56. 51.100
  libavcodec     58. 91.100 / 58. 91.100
  libavformat    58. 45.100 / 58. 45.100
  libavdevice    58. 10.100 / 58. 10.100
  libavfilter     7. 85.100 /  7. 85.100
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  7.100 /  5.  7.100
  libswresample   3.  7.100 /  3.  7.100
  libpostproc    55.  7.100 / 55.  7.100
Input #0, matroska,webm, from 'test.ac3':
  Metadata:
    title           : test25.ac3
    encoder         : libebml v1.4.1 + libmatroska v1.6.2
    creation_time   : 2021-02-12T03:41:58.000000Z
  Duration: 00:01:00.00, start: 0.000000, bitrate: 193 kb/s
    Stream #0:0: Audio: ac3, 48000 Hz, stereo, fltp, 192 kb/s (default)
    Metadata:
      BPS-eng         : 192003
      DURATION-eng    : 00:00:59.999993088
      NUMBER_OF_FRAMES-eng: 1875
      NUMBER_OF_BYTES-eng: 1440000
      _STATISTICS_WRITING_APP-eng: mkvmerge v53.0.0 ('Fool's Gold') 64-bit
      _STATISTICS_WRITING_DATE_UTC-eng: 2021-02-12 03:41:58
      _STATISTICS_TAGS-eng: BPS DURATION NUMBER_OF_FRAMES NUMBER_OF_BYTES
Stream mapping:
  Stream #0:0 (ac3) -> channelsplit
  channelsplit:FL -> Stream #0:0 (pcm_s16le)
  channelsplit:FR -> Stream #1:0 (pcm_s16le)
  channelsplit:FC -> Stream #2:0 (pcm_s16le)
  channelsplit:LFE -> Stream #3:0 (pcm_s16le)
  channelsplit:BL -> Stream #4:0 (pcm_s16le)
  channelsplit:BR -> Stream #5:0 (pcm_s16le)
Press [q] to stop, [?] for help
Output #0, wav, to 'front_left.wav':
  Metadata:
    INAM            : test25.ac3
    ISFT            : Lavf58.45.100
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, 1 channels (FL), s16, 768 kb/s (default)
    Metadata:
      encoder         : Lavc58.91.100 pcm_s16le
Output #1, wav, to 'front_right.wav':
  Metadata:
    INAM            : test25.ac3
    ISFT            : Lavf58.45.100
    Stream #1:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, 1 channels (FR), s16, 768 kb/s (default)
    Metadata:
      encoder         : Lavc58.91.100 pcm_s16le
Output #2, wav, to 'front_center.wav':
  Metadata:
    INAM            : test25.ac3
    ISFT            : Lavf58.45.100
    Stream #2:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, mono, s16, 768 kb/s (default)
    Metadata:
      encoder         : Lavc58.91.100 pcm_s16le
Output #3, wav, to 'low_frequency_effects.wav':
  Metadata:
    INAM            : test25.ac3
    ISFT            : Lavf58.45.100
    Stream #3:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, 1 channels (LFE), s16, 768 kb/s (default)
    Metadata:
      encoder         : Lavc58.91.100 pcm_s16le
Output #4, wav, to 'back_left.wav':
  Metadata:
    INAM            : test25.ac3
    ISFT            : Lavf58.45.100
    Stream #4:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, 1 channels (BL), s16, 768 kb/s (default)
    Metadata:
      encoder         : Lavc58.91.100 pcm_s16le
Output #5, wav, to 'back_right.wav':
  Metadata:
    INAM            : test25.ac3
    ISFT            : Lavf58.45.100
    Stream #5:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, 1 channels (BR), s16, 768 kb/s (default)
    Metadata:
      encoder         : Lavc58.91.100 pcm_s16le
size=    5625kB time=00:01:00.00 bitrate= 768.0kbits/s speed=94.4x
video:0kB audio:33750kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown