[FFmpeg-user] demuxing and re-muxing of mxf video files

[Paul Tapper]

Hi,
I hope this is the right place to post this question.  Sorry if it isn't.
I'm trying to use FFmpeg to take an .mxf file and:1. demux the audio out of it to a .wav (and then process the .wav myself), then2. mux together the video from the original .mxf with the .wav that I have now processed, to get back to an .mxf file, as similar as possible to the original .mxf, but now with my processed audio, instead of the original audio.
I've got step 1. working with a very simple:
ffmpeg.exe -i "test.mxf" "test.mxf.wav"
but I'm a bit stuck on step 2.
I've tried the following:
ffmpeg.exe -an -i "test.mxf" -i "test.mxf.wav" -vcodec copy "test.mxf.remux.mxf" 
but I get an error "[mxf @ 01EF8610] track 0: could not find essence container ul, codec not currently supported in container"
Please could anyone suggest what I should do here?  Is this even a sensible thing to attempt with FFmpeg?
Thanks
Paul