In the "for what it's worth" department, here are my views. From 1989 to 1994 I owned a pair of M802S2's; in 1995 I went to Matrix 800's, and in 2002 I went to Signature 800's. The Signature 800 is the flagship of the Nautilus line.
I believe that with N803's, and probably N804's, you'll find a huge improvement in musicality over the Matrix speakers--which themselves were no slouches. As the N804 is a floor-standing N805, I'd go with the N803 if you can. I'm a big fan of B&W, and I feel that, without a doubt, the Nautilus line are the best speakers B&W has ever made.
I believe that with N803's, and probably N804's, you'll find a huge improvement in musicality over the Matrix speakers--which themselves were no slouches. As the N804 is a floor-standing N805, I'd go with the N803 if you can. I'm a big fan of B&W, and I feel that, without a doubt, the Nautilus line are the best speakers B&W has ever made.