rib61 - You have some fine speakers already. If you're really just looking for a bass boost then HSU, SVS, REL, et. al. might be able to help for maybe ~20% (or less...) of what that whole D3 "upgrade" would cost you. If nothing else, you'll get to play around with what will likely be a very fine subwoofer unit. And if, in the absolute worst case, you decide you just don't want that new toy then you should be able to sell it off for a decent price.
Heard the B&W N804d3s ...
I've owned the original iteration of the N804s since I bought them new in '01. After 15 years, I thought perhaps it was time to upgrade to a newer model. So, I auditioned the new N804d3s at a local retailer. They sounded great, and are an improvement over the originals in the areas of bass slam and airiness. However, that step up to my ears is equivalent to about 10-15%. Not sure that that sort of improvement justifies the price ($9K for the d3s vs. $3,500 for the original N804s), although "upgradeitis" tempts me to pull the plug. Is it just me, or does the law of diminishing returns apply in this case? Your thoughts on this or the qualitiative differences between the old and new Nautilus lines would be most appreciated.