Pair of REL T5/Xs works quite well with my 10'x16' room. These accentuates just enough bottom end of the SHL5+. I've got the RELs about 8" off from each corner walls. No need to aim towards MLP since they are down-firing drivers. This was confirmed by REL support. I'm amazed how nice they complement the overall soundstage. Unplugging the speakons on both subs during playback tells you right away that something is missing. They just sound right with them on. No bloat.
Once you run them in with the recommended track from Sneakers ST, stream John Williams' album At The Movies - the album tracks will help you exhibit the clarity and musciality of bass done right.
That said, don't expect the bone-shattering effect like a 15" HT sub would do, but there are certain tracks that the T5/Xs - to my surprise - rattled the windows.
Enjoy the new gear!