Right now I have Magneplanar Ib's on the sides and the Magneplanar MGCC1 (their first center) in the middle. Because the speakers aren't identical, there is some timbre change in pans, but there aren't many places where it comes up in movies. My rears are still Boston Acoustics A40 Series IIs, and, no they don't match. It's not much of an issue for HT, but for SACD it's a problem. For a long time I had Bostons all around, which worked well, but I had to become very good at repairing woofer surrounds, and I had to replace a couple of tweeters. Parts are readily available on eBay, fortunately. There's a longer story about this, and it involves our visit to the Hsu audition room, but that's good enough for now.
However, I still long for the days of identical speakers all around. What I've found with the HB-1 Mk 2 is that the size and price are attractive, and they have very good sound (although a Chopin recording this afternoon has started to make me wonder again about the highs). The HB-1 can play loud. What I notice with many speakers, and amplifiers are probably part of the equation, too, is that massed violins playing fortissimo tend to break up a bit, and large choruses have problems. I think the sound of a large chorus is something even the best recordings and reproduction equipment still have trouble with. If you've ever heard, say, Mahler's Sym 2 or Beethoven's Missa Solemnis in concert, then you know that recordings never get it quite right.