I have been trying to figure this out for some time now. I just got Action! the other day and no matter what settings I use the audio will not record. I have gone so far as to try and record only the audio file (rather than with video) only to see that the audio files are 0 bytes when finished. I also have the mp4 lockup after ending recording, but it looks like that is being investigated.
RAM: 32GB Ripjawz@3000
MOBO: ASUS ROG Rampage V Edition 10,
HDDs: 512GB Plextor M8Pe x2 (SSDs), Kingston 120GB SSDseagate 2TB hybrid drive, 4TB WD Black.
GPUs: 2x 980 Ti
I can get video to record in AVI (not ideal for me) but sound is non-existent. I would love to use mp4 and mp4 sound. I use the realtech onboard sound as it is actually fairly decent.