Nick, I had a 4BSST driving a pair of 803's and switched to a Musical Fidelity KW500 - didn't try the A5. The Bryston was certainly well made but found it too bright on the top end with my B&W's, the KW500 has tighter bass, cleaner highs and separates out individual instruments and voices much better. I don't know how the A5 would stack up, so if you can I would try and listen to the two amps before making a decision.
Another option is to look at some of the non-mainstream amps on this site, such as AVA and others - better value options?