The new Bryston 'squared' lineup is great. Even the SST (just before the square upgrade is pretty good. Anything prior to SST is just ordinary.
I own Magnepan 3.6s and Bryston 4B-SST2 (also Bryston BP-26)
And can say I am pretty fussy about the quality of sound, and the Bryston is right up there. Some subtle variations in different (top quality) amps may make an audiophile choose one brand or another, but for the current Bryston lineup, no compromise in sound quality compared to any of the competition at the price points of the different models.
And IMO The comment by a dealer is pretty suspect if they do not carry the brand, or if they want to push some slow selling different model.
If you see the current show, the Magnepan rooms have two setups, Manepan with Bryston, and Magnepan with Audio Research, both great with Magnepans.
Bryston is the #1 recommended amp for Magnepan from the owners of Maggnepan speakers.