Combining 2 channel audio and home theatre

Adding a separate stereo amp would likely help, but the Denon’s preamp section will continue to be a significant bottleneck to achieving better 2-channel performance as long as it’s in the signal path.  Period.  Preamps matter!!!  The easiest, most cost-effective way to do this would be to get a good integrated amp.  Something like a used NuPrime IDA-8 would be a nice step up in performance from your AVR, and it also has a good onboard DAC so all you’d need would be a streamer.  A used Bluesound Node 2i would suffice nicely without costing very much.  Just one option, and best of luck. 

I have found a way to do this. Makes a world of difference. Have a 3.2 setup, which is conducive for my listening setup. For now. 
Focal Sopras front L and R are connected to my Luxman 509x. Center sopra is connected to a Peachtree amp500. My streaming source is a Aurender A10 which is connected to the Luxman. REL 212SE x 2 are connected to the Luxman via high level inputs. LFE inputs from the REL are connected to my Marantz SR 7010 subwoofer outputs. My Marantz then acts as my preamp only. And needless to say, the LCR channels are connected to the pre-outs of the Marantz and the respective inputs on the Luxman and Peachtree. When I wanna watch TV/HT, I use the Luxman’s HT bypass switch. It’s called ‘seperate’ on the Luxman remote. Other manufacturers call it HT bypass, Direct Input, Mains in, etc. And switch it off so I can stream music from the Aurender through the Luxman for 2-channel only. 
It would essentially be the same setup for a 5.1, but with more speakers and separate amps to drive them, all connected to the AV receiver or Pre-pro for HT use, and simply switching the HT bypass switch back to off for only 2-channel listening. This way, as someone mentioned, I’m not dependent on my Marantz preamp for my 2-channel listening, but rather on my Aurender’s...If you want to expand your soundstage by using subwoofers for both HT and 2-channel listening, options are limited. For me the RELs make perfect sense here, because of separate high-level and LFE inputs. Best of both worlds I suppose.. Sorry if my description is a bit confusing.. 

Mass.market surround sound receivers haveway too much stuff going on for too low a price
 And all.of that circuitry impacts resolution

 is not that the denon cant drive the dpeakers it is that a more dedicated two chanel piece will.sound way better 

Wesell.most integratedhard to beat the nad for agreat built in streamer

Dave and troy
Audio intellect
Nad, nuprime deelers

Keep it seperate, sound will suffer. Jmo. I have a totally different set up for watching movies. My hifi Is completely independent from the surround sound/home theater etc. Dedicated 2 channel hifi with no subs. If speakers can’t go low enough on their own, then imo they should be replaced with a competant pair.

+1 on the integrated amp with HT bypass as the best approach. It’s just the $700.00 budget that is a problem. Ideally, you’d like to get Tidal from a device that can be shared between the AVR and the amp...Node 2i or older 2 can work, but that’s half or more of your budget. A Rega Elix-R would be a nice choice, but is way over the limit. A used Rotel A-12?  Really, enjoy what you have until budget permits you to get the gear you want, or an anonymous benefactor gives you a gift of a discarded amp.