I've often wondered about this. I have a BK200.7 and when I purchased some Emotiva XPA amps and used the combination of the amps, running the Emo on my front mains, Audyssey just turned down the gains on the Emo during auto room correction. When I disconnected the BK 200.7 and just ran the Emo (much higher power than the BK), I found that I had much more power at my fingertips post room correction implementation. So while the theory behind using the A51 for the front, sides, and center seems sound (pun intended) while running the 8077 on the rest of the surrounds, I wonder if you will be limited to the weaker of the two amplifiers with respect to power output. Obviously other advantages of the different amplifiers would still be realized, such as dynamic headroom, THD benefits, etc.
Well, the A23 is less powerful anyway compared to the A51 (and I don't need anything more powerful anyway ).
Power Output (8 Ohm): 150W (20Hz - 20kHz, 0.08%)
S/N Ratio: 105dB
Power Consumption 800W (Standby: 0.4W)
Continuous power output: 125 watts RMS x 2, 20 Hz - 20 kHz, 8 Ω, both channels driven
S/N ratio: 112 dB
Power Consumption 700W (Standby: 25W) [x3=2100W with 3 A23s ]
Here are my 'ambiance speakers:
Kef Model T 101 (wides, front height)
Frequency response 80Hz - 30kHz
Amplifier requirements 10 - 100 W
Sensitivity (2.83V/1m) 90dB (wall mount)
Maximum output (SPL) 107dB
Kef Model 60S (Rear)
Nominal impedance: 6ohms
Amplifier requirements: 10-100W (into 4 ohms)
Frequency range: 120Hz to 20kHz +/-3.0dB at 2m on reference axis
Sensitivity: 87dB at 1m on reference axis for a pink noise input of 2.83V (anechoic conditions)
Maximum output: 107dB on programme peaks under typical listening conditions
So it looks like either amplifier is more than powerful enough. The Parasound will be a better amplifier, but uses much more energy and takes up more space.