If you can find Quad ESL 63's with latish serial numbers, Nick Gowan of True Sound, Campbell, CA does a fabulous upgrade that involves replacing 62' of internal wire, among all the more obvious things. Without knowing the famous Crosby mods, I shouldn't say which are best--but I can't imagine that the Gowan upgrade can be beaten or even matched by them. Web address: www.tsound.com. It might be worth looking into. (I should add that Nick upgraded my Quads, and it was one of the biggest improvements in my sound.)
