So what are the compromises multichannel processors make that undermine achieving that end?
Where to start? Ok, noise is a good one. Having the delicate stereo signal in the same proximity to all the noisy digital processing, etc. going on in an AVP is to say the least suboptimal. Then there’s cost. If you’re selling a $6k AVP, how much of the parts cost goes to the stereo preamp and how much to the processing, other channels, etc.? Answer: not much. Of course, this includes the pivotal power supply that if not shared with the AVP is usually specified to meet a price point rather than for better sound. So, putting a good stereo preamp in an AVP would raise the cost to the point where most people looking for a multipurpose system would balk. There are some very good AVPs out there, but now you’re looking at >$10k, and what are the odds the preamp section in those AVPs is a good match for both your tastes and the rest of your other prized stereo components? Good luck with that one. Speaking of power supplies...
The best solution is separate power supplies, but that’s an impossibility that’ll never happen.
Which brings us back to “if you only knew what you were doing.” Given your arrogance I’m not inclined to waste the time explaining it here (maybe another more charitable member will), but it’s absolutely possible.
Admittedly, I obviously have no idea what I’m doing. However, I’m satisfied with the results of my ignorance...people who use music to listen to their components in the belief they can buy and confect a system that will give them "realistic" sound reproduction are delusional...
I agree wholeheartedly you obviously have no idea what you’re doing, and that’s absolutely fine if you’re “satisfied” with your results. You are the reason I included “If you’re happy with the stereo performance of an AVP or AVR then rock on and it’s all good” in my prior post. But if you think “realistic” sound is a pipe dream then it’s you who are delusional and you really need to go listen to what a really good 2-channel system is capable of because a truly good one can drop your jaw to the ground. But ignorance can be bliss — I’ll give you that.