Question on 2 channel vs 5 channel amps ?

I can only speak from a similar experience. I had been using a Mcintosh MC7205 5 channel amp and decided to get a Mcintosh MC352 2 channel amp for the front. This resulted in a much improved sound but the 352 added a 150 watt advantage. But the 7205 is running considerably cooler with a channel idle between each used channel. I feel that the two channel amp isolated the power supply usage and lets the two channel listening be a little more pure in reproduction.

I have the current Sherbourn 5 channel amp in my video. I tried my Aragon 4004MKII for the RH & LH front channels. It did seem to sound a little better all over. It should, it cost as much as the Sherbourn when it was new. The Sherbourn has 5 discrete monoblocs in one chassis, like the Bryston 9B. I believe that's why it sounds as good as it does...............
I'd try to pair it with the current Bryston 4BSST or the 4BST, there are plenty of the STs for sale here on Audiogon.

I have never listen to any Sherbourn amps so I don't know what they add or subtract from the big picture. You could do what many of us have done, add a two channel pre: passive or active with pass through for two channel. I don't know for sure, but I would think this may sound better for two channel sound.

Get the two channel amp from the same maker.
Otherwise, you'll hear a tonal balance shift in multi channel mode.

I dunno which one comes closest to the one you have. Those three
you've listed sure sound diffrent from one another.