Amp/Preamps vs. High end AV Receivers

If this is for 2 channel listening, there are no high end av receivers, too much compromise toward av. I have had a few onkyo/Yamaha av receivers and the  onkyo’s Seemed to have a more warmer sound. 
You will do far better getting an integrated amp like the new yamaha’s for the cheap or go up to the hegel’s for better sound quality. You will still get the built in dacs plus a few other features but the sound quality will be much better for 2 channel

The OP just stated that 2 channel is not his priority and he's using his system for mostly surrounds.

If you like Onkyo for rest of the capabilities then just get a high powered low cost 5 channel amp that can do 2 ohm stable like ATI AT525NC. Small form factor , no heat, excellent measurements. You can spring for newer hypex models but they will be more expensive than ATI. 

For a great deal contact @apexstereo .

You can continue to upgrade AV when you see fit and the amp will keep your speakers adequately powered. Frees up your choice of AV in the future.

I can't afford really high-end expensive gear but that being said I have my "analog" system which consists of Emotiva separates which cost about the same as my Denon w/atmos and neural x for home theatre. About the only difference my aging ears can tell is that Emotiva separates seem to have better low end or more precisely go lower.

I've not found that inexpensive speakers mean that there isn't a benefit from better electronics. They seem to benefit quite a lot.
Regardless of what is being played- HT, music videos or 2 channel, my prior comments apply regardless. In a nutshell, **all** single-box audio systems are compromised in order to get everything in one box. The more the separate aspects of a HT system are broken out to separate components, the more **potential** exists for vast improvement.

Back in 1999, Stereophile, at a Stereophile Show in NYC, set up two Home Theater rooms side by side. The two rooms were identical (being in a hotel) and the video equipment was identical as well. One used a regular home theater receiver/processor, the other used separates. A poll that they took showed that 90% of people visiting both rooms thought that the room with the high end audio system had a better picture!