The difference between gain and power rating is fairly straightforward. Bryston amps have a switch that changes how much more voltage the amp puts out relative to the preamp. So, lets say the pre-amp is putting out 1 volt at any given time, the amp will increase that one volt by 23 or 29dB depending on where the switch is. In other words, the gain of an amp dictates the proportion of output power to input power.
The power rating of an amp dictates up to what power output that proportion can remain true without the amp running into clipping. So, you can drive a higher power amplifier harder (thus putting out more power) than a lower power amplifier. A BP-26 pre-amp, for instance, can output up to 30 volts from the balanced connectors. You couldn't get anywhere close to that without clipping 4B - only about a 10th of that. A 28BSST can take more than twice that much before clipping.
Mixing power amps in home theater and bi-amp situations is common however you need to be able to use amps of the same gain or (as in surround processors) be able to adjust the gain of individual channels to compensate for inherent differences in amps. If you were biamping a pair of Middle T speakers, for instance, you might use a 14B for the bass sections of the pair and a 4B for the mid/tweeter sections of the pair.
Does this help?
