HT and 2 channel in same room? 1 or 2 systems?

I have been using 2 systems in the same room for 20 years: This way each system can be optimally set up. To get the best HT performance, you need to have a wider placement of the main speakers which in most cases will adversely effect 2 ch performance. The 2ch setup does not provide the big expansive wall to wall sound because of width restraints. Another problem is there is no dedicated center channel speaker to match the LaScallas. This would most likely would cause the center speaker too not blend in and always be localized. The woofer problem is easy. Almost all RELs from the original company from the Richard E Lord days will have 2 dedicated inputs that allow high level and low level connections, each with dedicated vol controls. So you can use the bass management in your avr for HT and the ReL crossover, high level for 2ch. Not sure if the new ReL company run by John Hunter will do that. I have been selling 2ch and HT for 30 plus years so I hope this helps you. I use this set up in my own home and it works flawless.

@kota1 

Thank you for the suggestions, especially the upgrade for Audyssey.  I have had that Denon AVR for a couple years but have never plugged it in.  I guess I didn't realize that it would take me a year to finish my basement / theater room.  I have a JVC projector sitting in storage that I've never plugged in either.  Same goes for the Oppo 103d BD.  Hopefully all this works as planned when I finally get it hooked up in a few weeks.  Fingers crossed.

I think the OP had another concern about how to set up subs in a dual use situation which is my concern also.  It was said earlier that using a sub that has dual inputs would work for this use case.  In my case, I found REL and Sumiko to be appropriate for this use case for 2 channel as well as HT.  Not sure how well they will work for this but it is their intended use by design.  I am not a big bass head, but do require it in my music and movies as I can easily hear the difference that subs bring to the stage.  My goal will be subwoofer integration into 2 channel and ultra low for HT.  I'm not sure about the latter with the Sumiko S-10's but I intend to DIY some 18's or 21's to help out with that and hopefully pick up the lower 20hz or slightly lower if I can get there.  I have heard that on a concrete slab, getting below 20hz is wishful thinking for me.  I'll give it my best shot.  Thanks to everyone for the information that has been put out that helps me and sorry to the OP if I may have hijacked some of your thread.  I believe we are both searching for the same answer to the same question.  Good luck to you.

@speed121

I was struggling with the same issue.  I decided that I would set up a home theater system and then add a two channel system off of front pre-outs of the HT receiver.  I wasn't to do that because when listening to music I don't want all of the signal processing in the HT receiver.  Also there are those who are saying that a good two channel integrated amp should should much better than a HT Receiver.  With the right integrated amp you can use the HT Bypass option on the integrated amp to essentially tie it into the HT system.... and then when you want to listen to two channel music you can shut off the HT receiver and just use the Integrated amp.  I also plan on plugging my streamer into the Integrated amp so that the HT Receiver is completely out of the mix.

Hey, I too have a multi and two channel rig in my living room. I use all tribe and analog for my 2 channel, and more modern great for multi channel. I have Klipsch corns matched with 6sn7 pre to el84 power amp, and use hi level sub. It is very dreamy and I would not go back. Now with that said the ht rig is no slouche. I use Maggie's all around in 5.1 setup with two large amps powering everything. Emotiva xmc2 for processing. I do use my dirac to eq everything and there's room treatments too. The Maggie's can be difficult with certain reflections on hard surfaces. So, my response to you here is that you may want to treat the room and give both rigs a good hard listen to make your choices. It could go either way but hearing about your 2 channel makes me think you'll want to keep both. Consider low powered tube if it's too bright for you at first. Hope this helps, cheers. 

Let's not make this any more complicated than necessary. If the Onkyo has preamp outputs for the front two channels, feed those to the tube amp and connect the Klipsh speakers directly to the tube amp. Don't connect speakers to the L and R terminals of the receiver. Now you have tubes for two channel and the reciever handles the outboard channels, the center, and the subs. The preamps in the onkyo are likely better than the power output stages, so let the Onkyo make the source decicions for you. If you have good FM stations in your area, you may find FM is as good as CDs. A happy surprise!  Happy Listening.