My guess is it'll be close enough. Ratings aren't exact. Brystons are supposed to test higher than they're rating, particularly the 4b. I used to use a pair of 3b's for my fronts (as monoblocks), which allegedly is supposed to produce the same power rating as one 4b (which I'm using now). However, the 3b's clipped at levels the 4b doesn't. That said, I bet by bridging 2 125 watt channels, you'll get close enough that boosting or subtracting via processor will be minor (and hopefully therefore not annoying). BTW, the 5-channel can't be made to bridge 2 channels without an interconnect splitter? I would have thought you could just tell it (via some switch or other) that you wanted a channel bridged into another one, the way you can do with most 2-channel amps. More fool me, I guess.
A bi-amping question
Right now I am using a Bryston 4B-ST for left/right channels in home theater. For center channel I am using an unmentionable monoblock. What I want to do is take my Acurus A125x5 amp that I have just lying around and bi-amp the center channel, using 2 of the 125wpc amps. Will this create the appropriate sound pressure level to match my Bryston?--or am I thinking about this the wrong way. Yes, eventually I will upgrade to all Bryston amps, but for now, I NEED to get the center channel level up. I do not like the result by boosting the level using the processor. The center channel is taking about 70% of the sound for movies and boosting it is just making it worse. For reference, I'm using B&W N804s for left/right, HTM-1 for center. These speakers matched for size, efficiency, frequency response and driver compliment. The processor (Proceed AVP) has only one center channel output, so I will have to find an IC splitter. Thanks.