Bryston 7B-SST vs. 14B-SST

Is there any sonic difference between the two? Is the 28B-SST worth the extra money. The amp(s) will drive a pair of Magnepan 3.6´s. What preamps are a good match with the (low output impedance) Bryston amps? TIA
Lets assume you are referring to the latest "squared" versions. If not then the 28B amps would be in another league.

The only differences I am aware of the 7B amps have a little more capacitance. Only you can know if the jump to the 28B amps are worth the cost differential. There are many Maggie 3.6 owners who have 14B or 7B amps and I would think that either amp would do you very well. Going with monoblock 7B amps does allow them to be typically placed closer to the speakers which may offer the opportunity to acquire "better" speaker cables if that's also on your list given you might now be looking for shorter lengths.

Can't go wrong with either as far as I am concerned. The cost differential to move to the 28B amps is substantial as in 2X the price or about $8K or thereabouts. You might consider upgrading another component in your system with that extra money that may in the end bring greater satisfaction...