Thanks for going in to that much detail
Kinda handy you had to open it up really!
The DAC specs seem pretty good which bodes well for sound quality and if you've got Bose then the built in amp IC doesn't really matter.
I wonder how noisy that fan will be - not much in there to cool really, but cheap chinese fans never seem to last very long. That might be something to upgrade later on. I keep wondering about taking a cold air feed from the hvac to cool the stereo down. B5 Passats actually had a pipe from after the evaporator which fed cold air in to the glovebox which was a great idea. Never seen it on anything else though.
Its a shame they put the optical drive in there really - it could have been 2" deep without it, instead of a big empty box.