apollo
Not being able to repro your problem is like shutting in dark ... but you should know that you have many other audio options for encoding: mp2, vorbis, flac, libopus, libvorbis, libtheora ... check all those to see if all are failing.
The fact that video only works is interesting ... but I don't know how to use this info.
Alternatively, if I remember right you started the development on an old laptop ... can you try the installation process on that laptop? use guc = 1 .... because is before iGPU8.
A second alternative (more complicated) is for you to try my new branch that has new transcoding scheme. The discussion was on this branch: tvheadend/tvheadend1792.
git clone https://github.com/tvheadend/tvheadend.git
replace with:
git clone https://github.com/uknunknown/tvheadend.git
git switch dev_new_transcoding