Re: CBM-170s or HTM-200s for side/rear surround?
In all honesty, if you're running a sub, I'd get HTM-200s over CBM-170s for pretty much anything.
The 200s are smaller, lighter, easier to place, look better, are cheaper to ship, and sound better through most of the range. They're actually pretty amazing for the price; the drawback being the lack of bass. The only thing I think the 170s do better is bass impact/extension, which is basically addressed in any HT application where you have a good subwoofer.
I'd just get four HTM-200s and call it a day.
Err, wait... you already have them? Well, then, go with what you have. It will make little to no difference which set you put where, so I'd let convenience of setup drive you. As noted, the 200s are easier to wall mount, so if one set has to be wall mounted, use the 200s for that, regardless of whether that's side or rear.
Luna Duo V2 LR, Titan Horizon V2, and Rythmik L22 & L12 in HT, Sierra-LXs in study, S-2EXs and Duo V2 C in bedroom, S-1 NrTs in dining room, S-1s at work, HTM-200s in kitchen. Brother owns CMT-340s and dad has a pair of CBM-170s.