Well, Gregm, my dream would be to be able to build a system with the Quads for the midrange, a couple of serious woofers, and perhaps two great tweeters. That said, it's not going to be easy. First of all, most of the subwoofers that you see around are made for the home theater market. I tried a velodyne foundation, 12 inches, and it just ruined the overall sound. I am now using it for my tv. I guess the ideal solution would be to have someone build a cabinet for two top-of-the-line drivers...something like, say, 10 inches. I don't think there are products on the market that one could buy with these characteristics, except perhaps for the gradient subwoofers that were designed for the ESL 63.
In reply to Sirspeedy, I love the Extrema's sound, an I agree with you that they are pieces of art. I guess my question is whether, absent the aesthetical pleasure that they give, one would buy them (and spend now around $ 6K) just for the sound...