Tried a Bryston 4B with Maggies

Yeah, I don't believe this guy either.

Isn't it 400w into 4 ohms? How could power be lacking?

Arh, just because a power amp has high wattage does not mean that power could not be lacking.
Power = voltage * current.
This amp could have a high (secondary) voltage transformer (that produces the 400W into 4 Ohms) but this transformer could have a very low current rating.
This would mean that this power amp would be (severely)lacking the ability to drive current into the speaker load making it inappropriate for use with current hungry speakers.
I believe (& correct me if I'm wrong) that Maggies, in general, are current hungry speakers. if the power amp cannot deliver current into such a load, the sonics are going to be anemic.
Hope that this makes sense....

J_stereo,

"(I like the Audio Research D300 better, but only marginally, and it was a much more expensive amp than the Bryston)."

Do you still have that amp? The D300 and the D400 have to be 2 of the most underrated SS amps I can think of. (When they were in production). If you still have one, how does it compare to newer amps? I'm just curious, I haven't heard one in a long time.

I don't think we have enough info here to make a judgement either way. I know Bryston makes very powerful amps but what if the OP has a really big room? Or maybe he's using a passive line stage and his source doesn't have enough gain to get the volume he needs. I can think of several more reasons as well, but without more input we just don't know.

The Bryston 4B was introduced in 1977, and appears to have been discontinued during the 1980's or early 90's. Kind of stands to reason that the poor sound quality the OP reported had something to do with its age and condition, assuming that the model number has been stated accurately.

Regards,
-- Al