AVP 2CH to dedicated 2CH....how big of difference?

OP you pose a very good question. I think the answer will be “it depends”. Though I’ve never had a high performance multi channel system, I have had upper level Marantz gear that I ran 2.1. I have also heard Dirac in some systems. My views/preferences may be entirely different than yours - so YMMV. 

Re Dirac - In my limited experience, I have heard the presence of the DSP on the signal. It didn’t sound transparent to me - but somewhat artificial.  Of course, it’s highly likely I’ve never heard it set up properly and  I don’t dispute the benefits of DSP in correcting some room issues.  But you have a treated room already.

Re Marantz gear - it definitely had/has a house sound and I found my upper end AV to sound harsh to my ears. I replaced it with PS Audio Stellar series gear (long gone as that was several system iterations ago so I’m working from memory here) but I remember it being a noticeable improvement in quality and clarity to me. As a second data point, I replaced a different Marantz A/V receiver in a simple 2.0 TV system with a nearly bottom of the line Hegel A/V receiver and it brought a surprising improvement in musicality and intelligibility. 

My suspicion is that upgrading your electronics to a higher performing dedicated 2 ch gear will bring improvements in clarity, musicality and spatial information (hall ambiance, imaging, etc.). It may not be earth shattering improvements and you may not like the results as much with the loss of Dirac, but given your room treatments, it’s absolutely worth finding a dealer who will let you audition the gear at home in your room with your speakers (which are quite nice BTW). 

And, I could be completely wrong and you find it isn’t worth the spend in $. But I firmly believe it worth the spend in time to find out. 

Best,

I submit you can have both by using a 2-channel preamp with HT bypass. I've tried to put together a decent HT system, but sold it to focus on my 2-channel. I had a Trinnov Altitude and Amplitude 16. I tried them for 2-channel only, but strongly preferred my Rowland components compared to Trinnov.

I have Dirac in my two channel system and in my 2 HT systems I have Anthem AVR.  I think they both add modest improvements.

a) Your first bottleneck is the golden ear,  it is a lackluster midfi speaker. On the other hand, a tekton epic 15 priced at a measly 2.5k/pair is a hifi speaker. A Yamaha NS-2000A is a hifi speaker. A mofi 888 is a hifi speaker, etc. Ya gotta know how to recognize a hifi sound somedays.

b) 2nd bottleneck is the class D ice diddly. Save it for surrounds and heights. Buy 3 Schiit Tyr monoblocks and deploy it for the front stage (front left, center, front right)

The Marantz AV10 is worth its weight in gold. Marantz is able to sell it to you for 8k because it is also subsidized for you by video enthusiasts around the world. If they didn't do that for you, price will become 100k. Gain stage the AV10 correctly. There is a learning curve associated with using it correctly. It is not some simple 1 trick pony preamp. Good luck.

Where I want to see improvements. On heavily dense tracks with a lot of instruments/layers, the sound stage can get very narrow. It doesn't collapse but I lose a lot of imaging. Two examples of this I can think of immediately are Comfortably Numb on the Pulse album. At the end with the crescendo and guitar solo...it can get congested and narrows. Same with November Rain Remastered. The beginning of that track is well layered side to side and front to back but at the end with everything hitting at once, I almost completely lose that image that I had throughout the first 3/4 of the track.

 

There is also a slight 'edge' to music. While this is excellent for movies (clear, distinct sounds) this can make music sound more clinical vs smooth and warm. I dont know if this is because its really an AV product and Im trying to do something outside of its wheelhouse, the ICEPower Class D crispness from the AMP10 or the revealing nature of the GE TRefs or a combo of all three.