I am definitely very much want to have as error-free transcode (and as little transcode as possible in general) as you, for same reason.

I am not sure you can absolutely trust ffmpeg for not doing any conversion by default. For example 6.1 seems to upconvert 16 bit audio when you select dvd_pcm audio output.

/dev/shm/ffmpeg/ffmpeg -i /home/guest/CIN51.mp4 -target pal-dvd -c:a pcm_dvd -f dvd /dev/shm/cin51.mpeg

ah, it only does so if decoder output floats by default (aac, may be mp3 too?)

for dv it was 16 to 16.

Not sure how good internal ffmpeg muxer for dvd file creation, but you probably can test this by reusing cingg created audio and video files from dvd master.

I have few more ideas to test and smart-up our bash script so it will use wav output + sox + mplex automatically if wav or pcm file was detected in output directory (so you can set easy wav output and do not care about BE pcm file and its extension), but again I need some time to test this.

I was looking for some quality control tools and found qctools and this post specifically on stackexchange

it mentions  program named Sonic Lineup, hopefully easy (and working on Linux) way to compare two audio files.

Not sure if it supports dvd audio tho ....

qctools are more aiming at video quality metrics, just build their latest tool:

I am sure you can get Appimage or even rpm from their site.