We use a Sony PMW-200 and shooting in UDF mode - 50 Mbps HD422 with 8 channels of 24 bit audio.
I would like to simply extract the audio files within the .mxf - how can I best do this? At the moment, we use USB to copy the .mxf files from the camera to a PC. Then import the .mxf in After Effects and then render just a audio .wav file.
Is there a better workflow? And what about exporting different audio channels?
No, this isn't really possible with off-the-shelf tools. We can access the raw, non-interleaved audio and video .mxfs when we record to optical disc but this directory is not accessible on the SxS UDF recordings. Even if it was they are not in the same .mxf pattern and can't be decoded easily. The best workflow is to continue exporting audio from the full res files. If by 'exporting different audio channels' you mean having more control over what channels get imported (for example, if you don't want all 8), this depends on the editor. Currently Avid and FCP 7 can do this but Premiere cannot. In Avid it requires a traditional import instead of using AMA. In FCP we tell the Transfer plugin to 'only import monitored audio channels' and then click the channel pairs we want in each clip's audio panel.