I have been a cinephile almost as long as an audiophile.
If you want them to share rooms, then you probably have to chose which one takes precedence. Putting a big monitor between your mains is a pretty horrible thing to do. I use a projector and a powered screen.
For me, this was my 2 channel system. I use the pre-out and I have used both HT bypass and and RCA switch (there are some very good ones, Manley probably makes the gold standard one).
I have the typical stereo - server > DAC > pre > amp.
My HT uses the same server, an AVR, and uses the pre-out to drive the amps.
I have very sensitive corner horns and I have used 25W amps to power these with great results in the past. My current amps are Manley Snappers (100W tube amps).
As for stereo using primarily reflection and HT using primarily absorption - this is pure rubbish. Both require pretty much exactly the same thing in terms of room treatment, and both require alot of it. The main difference is in speaker placement, and how the speakers interact with each other and the room.
When I set up my system, I focused on front speaker placement. The rest of the speakers went where I could fit them, and I let the DSP figure out the timing. Not ideal, but still extremely good.