I have a pair of (much improved) ESL-63 Quads, and recently got a pair of your new ribbon tweeters, after hearing them on a few horn systems over friends houses during the recent Colorado Audio Fest.
My initial impression of your speakers on the Quads was not favourable. No matter what I did, my speakers simply sounded more natural without your tweeters. However, the other day, I went back and re-read the instructions, with particular emphasis on the issue of speaker phasing. Much to my surprise, and delight, reversing the leads from the tweeters into the Quads (positive of tweeter connected to negative of Quad etc.) did the trick. Apparently, when connected in normal fashion the tweeters were out of phase with the Quads. I am now enjoying the added magic of your speakers which I would enthusiastically endorse with ESL-63 WHEN connected as noted. I sent this so that you could alert other Quad lovers.