The Bryston amplifiers have a switch on the back to alter he gain to either 23dB, or 29dB. Matching the gain to the RCA, or XLR.
When I had Magnepan 3.6 (for 8 years) I found the 23dB gain position (using XLR in) on my 4B-SST² to be a bit subdued compared to the 29dB gain, which had more definition and 'pop'. So even though I was using XLR in, I used the 29dB switch position.
Well, with my new Magnepan 20.7 to same amp in the 29dB position is a bit edgy, and so I tried the 23dB and now just right. Smooth and clear.
Always pays to fiddle with stuff.