Re: CBM-170s (L/R) + HTM-200 (C)?
I bought a pair of HTM-200s last year because I needed some speakers I could place horizontally. The HTM-200 is an excellent little speaker—the only real knock against it is that it doesn't go very deep, but that's what you're going to get with 4" drivers in a sealed configuration. But mostly what you want out of a center is dialog, and they're great for that.
As N Boros, said, they'll match with the 170s, no issues there. A pair of 170s and a 200 for center is a great starting configuration.
Next thing you really need is a sub. WAY more important than surrounds. Even a small sub (so as not to annoy the neighbors) will be a good addition.
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.