This modest (by Audiogon standards) system was built up slowly over time and though I'm fairly happy with it, I wonder about the next step. I listen almost exclusively to classical music.
Listen to a Bryston 3B ST or 4B ST power amp with the Maggies and I think that you'll be changing out the power amp as soon as possible. I agree with Rgd that the .5b would be a likely target for upgrade, but I would not hang onto the B&K 4420 any longer than it takes to get an ad going on Audiogon. You might want to listen to a Jeff Rowland Model 1 or Model 5 also. They are really best when you run a balanced preamp in front of it, so the ARCAM might need to go in favor of a CD with balanced outs.
I would look at changing out the Bryston .5b preamp. I had one for many years mated with an old 3B amp. Now I have a 4B-ST with a tube preamp (Rogue 66) and I love it. I think you should audition a tube preamp and that should warm up the sound nicely - if warmth is something that appeals to you. Another way one could bring a little more musicality to your system would be to try the Njoeb 2000 cd player - available from Upscale Audio (no affiliation here and I do not own one) but understand that they have been getting a number of great reviews.