New theater build questions

Been looking looking at some of the newer marantz and integra processors as well.

In the sub department, I've owned a SVS PB13 ultra in my 13x19x8 room and it was amazing. Parted with it to buy 2 when I renovate room to 20 x 25 x 8. I may do 2 svs SB13ultras or one with bigger driver than my Casta C's. Two subs are better than one always.......

I've also owned the Emotiva UMC-200 and it was really good through 5.1 multi channel analogue. It's processing sounded better than the Oppo 105 I had and sold.........could I suggest an Emotiva XMC-1 and be done......

I like my Airmotive desktop speakers, I am really thinking about Dolby Atmos though, it would cost be a bit extra, but is it worth it? Something like one of these http://www.bigpicturebigsound.com/Buyers-Guide-Dolby-Atmos-Receivers.shtml

Obviously you have liked what you've heard from the DCM'm in other setups. That said, I personally would strongly recommend you look at other considerations instead of the DMC music speaker choices/types of loudspeaker up front, all together?! (especially with your low 7' ceiling, which will have you hearing way too much reflection vs direct, smearing imaging, lessening dynamics, focus and sound-staging, obscuring detail, etc). Might I recommend looking at more efficient, dynamic, multi-woofer/tweeter designs, and possibly ones with powered woofers or active drivers?! (think, more HT effective loudspeakers with more presence and focus, which also sound great for music??)
Personally, I've sold/used/installed/auditioned just about every kind of HIFI over the years, with lots of experience in custom hiend, as well as audiphile/acoustics guy. And I honestly think most people would be thrilled with the performance of something like a Def Tech powered woofer tower loudspeaker, driven by separates, yes, and a tube 2 channel preamp front end, in your type of set up, yes!! With careful setup and acoustics considerations, the sound should be very high quality, super dynamic, focused and solid for HT, and I doubt you'd ever hear a complaint from anyone listening to music from that setup!!
Of course you could get "marginally descent sound" from pretty much any loudspeaker choice, and there's simply a ton of ways to do your setup/system WRONG! (Lackluster performance with most of what you'd try) Cause the problem however with typical single tweeter over woofer stereo "Music" loudspeakers, is they're typically too laid back and open sounding, aren't so "room acoustics friendly"(your low ceiling kills the sound of open dispersion design speaker sound quality!),lack that immediate presence to the sound as in commercial theaters, and large ones don't handle power (definitely not BASS) as well as active versions!
Believe me, if I thought you're DCM's were a great fit, I'd whole heatedly recommend for your setup. I'd honestly give em a 5/10 for performance across the board given your parameters. I just think (I know) you could do much better overall with the right selection and proper setup. (think "Active/powered" Wilson WATT Puppies as the goal for ultra high end here!..othewise 4 cheapo, go with what I said as a consideration) .
Powered subs? (if not going active subs built into a speaker)- I suggest couple of high output SVS powered subs up front on centered wall (slightly off), maybe some EArthquakes, or a Paradigm Servo, MK MX5000, etc? Otherwise, multiple powered smaller subs all around the room for all channels is too much of a Cross to bare?!...
Yes, separates system over receiver, for sure. Work acoustics, proper setup such as 1/3,1/5,1/7th locations for seating, and 1/6,1/10,1/14th positions for loudspeakers for pretty fool proof foundation. research Russ Herschelmann and Anthony Grammani for acoustical and set up help, and check out Andrew Robinson's IMAX youtube series for more helpful setup ideas!

Hope that helps