Yes, they will work well especially if you get another one and have them in bridge mode. The Mani's need a ridiculously large amount of power to get them to really sing. 500w @4ohm will work well, which the 4b will give you. I bet however two 4b's will give you a large improvement.
I had the A5.5 Musical Fidelity integrated amp with 400w@4ohm and it was not enough although it did sound good, it was ultimately missing the magic that Mani's are known for, something I heard when I had Roland 7 mono's a while back. Your Bryston separates will give you more power than I had with the A5.5.
I say go for it.
Cheers