What speaker to replace ESL 63?

Without a doubt the best speakers I can suggest to replace them with are the Piega P-10's. The have ribbon tweeter, a ribbon midrange and cone woofers. This is easily one of the most coherent speakers I have ever heard. It is much better than the Quads in the midrange and has some of the best bass available. The dynamics are also top notch. It is the first speaker that gives me the best of cones and ribbons.

They will surprise you!

Ditto above, Detlof & Jtinn. Also suggest you add Soundlab to your short-list. The 1 or 2, depending upon yr amps' driving power (the bigger ones are very expensive I beleive). Detlof would know more than I on how the SLs compare w/ Quads.

Cheers!

Our recommendation would be to audition the new Quad ESL 988, the Magnaplanar 3.6, and the Avalon Opus. These are all excellent fast settling, low distorsion designs. The choice will depend on your taste, and your associated components. Chances are you would favor the ESL 988.

Been there, done that! Love the Quad's but
they are just too fragile. I am now living happily
with Harbeth Monitor 40. Simply accurate, musical
and easy to handle, well, at least you have better
dynamics than the Quads.

The Harbeth Compact 7 is a closer fit, I think, and a lot less $.