Joeb:
Great system you have there. The electronics you have are very good, as are the interconnects.
One question though.......... Are you running your B&W Nautilus 804's full range, or are/were you planning to cut them off at a certain frequency and then letting a sub take over???
Because if you are doing that, then I would guess that if you are set on using a sub, then I think that something like an REL Strata III (at least) should do the job. If you are on the other hand, thinking about replacing the speakers themselves......... then the only speakers that I can think of that has the bass response that you want, that also doesn't cost a mint would be one of the Vandersteen models (if you had a system like mine (KEF Reference 102/Adcom GFA-545 Mk II/Adcom GFP-750/MITerminator 2/MITerminator 3), then I would say the starting point would be one of the "2" models (either the 2ce or the 2ce Signatures). But since you seem to have higher-end electronics than I do, then I think you should start with one of the "3" models at least, working up to the "5" if necessary). Try that first to see if that gives you the improvement you are looking for.
But also, I would also think that a CD Player upgrade is in order. The "LEAST" expensive CD Player I would consider would be an Arcam CD72. Either try that first, or a Rega Planet and see if that would gives you the improvement you are looking for. If either of these players improves the bass response that you are getting from you B&W Nautilus 804's, then you may have solved the problem then. If not, then I would go ahead and address the speakers at that point.
Good Luck........
--Charles--