Bryston 4B-SST vs. 6B-SST


Within the next month or so I plan on upgrading my two channel amp, currently a 4B-ST. You can see from my "system" link that I have a home theatre setup, but, I primarily listen to 2 channel.

I currently have the 4B-ST on the front two channels and a Rotel RMB-1075 (5x120) bi-amping the center and a single channel to each rear. This of course leaves one channel unused.

I like the way the 4B-ST sounds, I really like how Pass Labs (X250) sounds but, budget limitations have nipped that in the bud, sigh. I do like the newer Bryston SST's a lot as well, and they are affordable to boot.

I have been able to audition a 4B-SST but not a 6B-SST. The specs are the same except for the 6B being 3 channels instead of 2. They do look different internally. The 6B looks modular while the 4B does not. It would work well if I could use the 6B-SST for the fronts and center and swap my current 4B-ST to the rears.

Has anyone compared these amps sound qualities, especially with 2 channel?

Do you think, or know, of any reason that would make the 3 channel amp perform less suitably in a 2channel situation?

Any thoughts are greatly appreciated.
distortion
For an update, I decided on the 4BSST. I made a few offers on used Pass X250s but no takers. The Pass is so deep, physically, that a new rack would be necessary. Surprisingly the SST isnt killed by the Pass, in fact its a pretty close race.

I decided to go with a 2 channel and a 5 channel Amp. The 2 for the stereo mains and the 5 for center and surrounds. I can biamp the center, run the two surrounds, and still have one channel left over for the rear center (6.1 setup). Plus I want the 2 channel path discrete for future upgrades.

All this is helped along by my loss of enthusiasm for multi channel hi-rez. I dont have, nor have heard, a single hi-rez disc in which I preferred multi channel over two channel. In fact, my modest Jolida CDP usually sounds better with the hybrid layer! Maybe that will change when funds become available for a source upgrade. Though redbook will be my main focus.

Secondarily I want to have some Vinyl experiments, which has my Wife all excited, BTW. When she figures out what that really means I'll probably have to take her shoe shopping or something.
I agree with you on the 2 channel part for stereo play back. Thats what I like about the most on my Sp 1.7. I have a great 2 channel preamp. I went to vinyl for 2 reasons. DVD and SACD selection. Plus I have gotten great NEW lp's off ebay cheap! I mean 6 bucks delivered! I even got 30 NEW old LP's for 14.95. I am only buyibg new LPs so I don't have to invest in record cleaning machine now. I'm very impressed with vinyl. I also decided to stay with my 4 channel amp for suround so my main amp will drive stereo. Buying a mono amp for 2500 bucks leaves me more money to put else where at this time.