Extract all audio channels as separate wave file from a multichannel file
for me the -map_channel option did the trick:
get the file layout using ffprobe multichannelinputfile.mov
    ffprobe version 4.1 Copyright (c) 2007-2018 the FFmpeg developers
  built with Apple LLVM version 10.0.0 (clang-1000.11.45.5)
  configuration: --prefix=/usr/local/Cellar/ffmpeg/4.1 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-ffplay --enable-gpl --enable-libmp3lame --enable-libopus --enable-libsnappy --enable-libtheora --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-opencl --enable-videotoolbox
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
[aac @ 0x7f903d01fa00] Assuming an incorrectly encoded 7.1 channel layout instead of a spec-compliant 7.1(wide) layout, use -strict 1 to decode according to the specification instead.
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'set1permeke.mov':
  Metadata:
    major_brand     : qt
    minor_version   : 0
    compatible_brands: qt
    creation_time   : 2019-01-05T22:00:13.000000Z
    com.apple.quicktime.make: Apple
    com.apple.quicktime.model: MacBookPro15,1
    com.apple.quicktime.software: Mac OS X 10.13.6 (17G4015)
    com.apple.quicktime.creationdate: 2019-01-05T21:58:54+0100
  Duration: 00:57:02.28, start: 0.000000, bitrate: 23693 kb/s
    Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709), 1920x1040 [SAR 1:1 DAR 24:13], 22756 kb/s, 60 fps, 60 tbr, 6k tbn, 12k tbc (default)
    Metadata:
      creation_time   : 2019-01-05T22:00:13.000000Z
      handler_name    : Core Media Video
      encoder         : H.264
    Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, 7.1, fltp, 928 kb/s (default)
    Metadata:
      creation_time   : 2019-01-05T22:00:13.000000Z
      handler_name    : Core Media Audio
[aac @ 0x7f903d019600] Assuming an incorrectly encoded 7.1 channel layout instead of a spec-compliant 7.1(wide) layout, use -strict 1 to decode according to the specification instead.`

I then mapped all the audio channels to seperate files for easier editing in my DAW
ffmpeg -i multichannelinputfile.mov -map_channel 0.1.0 ch0.wav -map_channel 0.1.1 ch1.wav -map_channel 0.1.2 ch2.wav -map_channel 0.1.3 ch3.wav and so on producing the asked for separate wav files