quad esl 63 needs a sub woofer

I have an quad esl 63 and I am planning to add a sub woofer. I need help about choosing one. I heard about gradient sw 63s. have anyone know anything about that. I am using tube amplifiers since I will need an extra amplifier to drive the sub, do you think eloctrocompaniet ampli (Class A)they match with the tube amplifiers. Thank you. Note:they are selling gradient sw 63pair( excellent cond.) for $1900. Do you think I should go for them?
Subwoofers spoil one of the best speakers ever made. None of them are fast enough. Have owned and sold ESL 63's for many years. Put your money in upgrading the front end of your system (better turntable/CD player)
I have owned 63's for many years and have listened to them in some other great systems. The purist approach of no sub's is great for some music but frankly doesn't do justice to full range music ie. symphony. You do need a fast sub (if such a beast realy exists) and you do also face trying to match a coned speaker with an electrostatic so the crossoveris equally important. I have stumbled upon the best combination that I have yet heard with a pair of Celestion 6000 subs that also make excellent stands for the quads. The cross-over that came with the subs works very well and for the fun of it, I also had a custom cross-over made that some recording/audiophile guy designed especially created for his studio. The 6000's are one of, if not the only, dipole subs manufactured. I am still not sure which cross-over works best but the sound is well integrated and I do not heard any appreciable loss to the Quads. I have no idea what the 6000's would sell for but at least this should give you another explore. For the true purist, switching a few cables gets you back to where some claim is the 63's true destiny. By the way, you might remember that Quad made some subs as well so maybe its not such a terrible idea. I hate e-male so my phone number is 517-673-8493 and the name is Denny.
Try borrowing a Velodyne HGS-12.