The AVR's are interchangeable commodity parts. Both the Denon 3808 (which I plugged into my system after my 4308 crapped its digital board, and for the record I still have both available to me, as the Denon has not sold yet) and Anthem MRX 300 are both competently designed, sonically transparent boxes. (The Denons both have considerably more power, which is why Anthem's propaganda about "beefy amps" or whatever is annoying. But both of them are adequate for most people's SPL needs.)
The only material difference between them is the room correction system.
No reasonable person would expect a sonic difference between two competently designed boxes with the same room correction system operating and calibrated using the same mike positions.
Yes, he does not have crappy speakers, but rather speakers with smooth power response (Orion, KEF, Revel) which means the Audyssey 2kHz notch will hurt his system. ARC may well improve it. Ditto Audyssey Pro.
No, I am stating facts
that flow inevitably from the the design choices of the room correction systems. Read Prof. K on the notch, and note that in in one post on the Audyssey FAQ someone asks him about how it would work with horns crossed at 900Hz. He replies "I don't know, didn't test it with such speakers." They seem to only have tested it on speakers with crappy power response (i.e. most "high end" speakers), not on competently designed speakers.
And what you seemed not to understand from my above post is that I contended that, using both systems properly, and using them speakers that have smoothly declining sound power, with the target curves set the same (either turning off the room gain on ARC or curve-drawing the same room gain in Audyssey Pro, and turning off the 2kHz notch in Audyssey Pro), there are not likely to be any material differences between ARC and Audyssey Pro. What differences there are are so minute that one would need a blind listening test to resolve them.
Now, between Audyssey with the infernal midrange notch (remember, one needs Pro to excise the thing) and ARC, at least on non-crappy speakers, the difference is obvious. One doesn't need a blind test to determine whether big frequency response differences right where the ear is most sensitive are audible, after all. I'll pick ARC every time.
What I write is obviously true to anyone who understands the target curves employed by both systems.
Again, if your speakers have smoothly declining sound power, there will be little difference.
If your speakers are brighter, Audyssey (Pro or standard) gives you a choice of target curves:
(1) roll of the highs to be more like a speaker with declining sound power (Audyssey standard curve).
(2) keep the highs basically as they are (Flat or Front). Also, in this mode if your speakers have smoothly declining sound power, Audyssey will boost the highs quite a bit.
Whether the difference constitutes improvement is a matter of personal preference.
By contrast, ARC as used in the MRX receivers does nothing (good, bad or indifferent) above 5kHz. So speakers with smoothly declining sound power will sound like it, and speakers that are voiced brighter will sound it.
Audyssey Pro adds to that a draw-your-own curve, though it doesn't have a great deal of precision in reaching it. (I think it's a 6dB window.) ARC lets one adjust the low end to account for natural room gain, but nothing else. The
2009 room correction comparison by Dr. Olive, et al., at Harman, which to date is the only objective and subjective comparative data publicly available on room correction systems (!), showed that listeners rather clearly preferred systems that allowed for natural room gain to be preferred by listeners. Ironically, given that a crappy loudspeaker (B&W N802) was used, the Audyssey 2kHz notch did not seem to help them in the Harman test, as the system adding that notch finished sixth, well below "no room correction used." (I do think Audyssey would've beaten no room correction if their standalone box also had DynamicEQ on board, though.)
