I've done X-LS alone, X-LS with subs, X-CS with subs, and now have X-SLS Encores without subs. My current room is almost exactly the size as yours, and it seems our use cases are similar.
First, is a second SVS SB2000 a possibility such that you could run them in stereo? My thought there is that if you like the heft/weight big floorstanders bring to the table, I might suggest X-LS Encores plus the stereo subs, because you may find positive results crossing the subs a bit higher so that they are playing into the lower midrange to get you there.
If the sub is really just meant as LFE fill for the movies and multiples aren't an option, I'd suggest X-SLS Encores with your existing sub. The X-SLS Encores dig deeper enough than the X-LS Encores that I think you may very well be happy when listing to music with just the speakers and not need the sub. Otherwise, you're crossing the sub in lower so the blend is maybe easier with just one sub, as it is really just filling in the foundation (and could probably play a little lower in volume overall, again just adding the last bit of spice to the metaphorical dish - key here that less is more so as not to overload the room).
The reason I wouldn't go X-CS in spite of the midrange advantages is because of the size of your (our) room. Pulling them out from the walls as you state you have (and I do) puts them pretty close to you distance-wise. My challenge with the X-CS when I ran them compared to the X-LS is the vertical off axis response. In my experience, the treble drops off more quickly in a much narrower angle with the X-CS than the X-LS, and sitting pretty close to them unless you keep your head firmly on axis vertically with the tweeter, you may likely hear some variation in the response with the X-CS as you move your head around (or if you share the space with family who are taller/shorter) that won't happen as quickly if at all with the X-LS (or X-SLS). Some don't mind it; for me it bugs me enough to now keep it in firmly in mind whenever demoing speakers.
That aside, if I were going to do X-CS, I'd really want a pair of subs to run them in stereo. The X-CS by themselves didn't play low enough for my tastes to satisfy me with the music I play, and in the long run I think I'd be less than pleased trying to run just one sub with them for as high as I'd have to cross the sub over to the X-CS to get the job done.