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

I went through this when I added video to an earlier system and again when I moved house and gear to a new location. Some of my conclusions:

1 - you need main speakers that are dual purpose, i.e. that have the range and sound good with either pure audio or video, which means that they have to have decent bass output - bookshelf speakers need not apply

2 - there is no such thing as a really good surround processor that will also do a truly great job in the pure audio system, so don't try.That means buying a good quality AV preamp or receiver and having a separate amplification chain for audio and video

I bought an Marantz AV preamp that does a very good job on movie sound but does not sound as good as my all tube audio chain.

3 - you can use the same power amp for thee main speakers if you like, or you can do what I did - use a different amp. That way I reserve tube life for music and use an old Rowland 5 solid state amp for AV - all I have to do is pull the speaker leads out of the tube amp and plug them into th Rowland

4. if you have a big room and your speakers aren't exceptionally good on bass, you will want some bass reinforcement, particularly as movie sound tracks use the impact of bass to stun their audience into admiration. That means a separate subwoofer (I use a pair of matched powered Hsu units that give good clean low bass, a fairly rare thing in reasonably priced subs.)

5. The AV preamp can feed a separate multi-channel power amp for surround speakers. You want decent speakers (I used all Vandersteen). Audition in the room to see whether or not you need a center channel speaker - it turned out that I didn't as my main speakers produced a better phantom centre channel than a centre speaker I had bought (and subsequently sold on)

6. - Pay someone with the specialized sound equipment to set up your speakers and room - it will ay of in the pure audio system as well.  Mark main speaker position with tape or marks in case you ever have to temporarily move them.  The analysis will also point out any slap echos and room flaws that you may want to address then or later - the solution may not be too expensive - heavy curtains you can close for movies, for instance can tame some problems.

If your main speaker placement in the room is wide enough that you can use a regular screen, you can buy a regular screen (mine is a 10 foot diagonal that is powered and winds up behind a false beam in the room when not in use.  If speaker placement dictates, you may need to locate the screen in front of the speakers (i.e. if they are placed closer together than the screen dimensions) in which case you have to but an acoustically transparent screen material (they aren't actually sonically transparent - they usually lose 1-2 dB but that can be compensated for when the sound guys sets it all up).

My set up can be seen at 

I am not sure of your specific questions other then the title, and that is pretty vague. I can share with you my approach when faced with the same general question where I had one space and wanted to optimize several factors - appearance, cost, sound quality for 2 channel . . .

I bought a Benchmark DAC3 with HT bypass. It has worked great for me. The DAC serves as a pre-amp also allowing me to input a digital signal from my streamer and also the analog signal from my Onkyo AVR. With a press of a button on the remote, I can be only two channels (digital input from streamer) using 1 amp and 1 set of R/L speakers.  Or I can switch to the analog inputs of the DAC which connect to the front two pre-amp out channels of the AVR . There are also outputs on the DAC and AVR for low level outputs for my two subs. I use a paired benchmark amp. I am very happy with the flexibility and sound quality. I find the two channel audio to be excellent and it is very easy to switch to the AVR inputs for TV/Movies allowing me to use the same two channel amp and R/L speakers.  The improvement over using the DAC/AMP in my AVR was very noticeable.  

OP, a lot of great suggestions here, many requiring $$. I agree with:

6. - Pay someone with the specialized sound equipment to set up your speakers and room - it will ay of in the pure audio system as well.  

Either that or buy the equipment and DIY. Do this first  with what you already own and it is much easier to proceed with anything else. 

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