Bryston is a great choice, because you can easily bridge it and get the most out of your amp. I use an old 4B for my passive sub.
What to use as a subwoofer amp
I am currently using a nad 218 to drive two SVS+ 20-39's. Do you think I am getting the most out of the subs using this amp. I know sub amps are different, but is that because manufacturers want to put everything within the sub, or are the class D and other types better for sub applications.