Hi John
I have not hard the ESL57, but owned the 63 for some years. I now use the Bastani Prometheus. For 3 years it has been MK1, but they'r upgraded to MK2 this summer. (I saw you post at audioasylum also)
My comment on the ESL63, is that it is a fantastic speaker. It's got a lightweight performance which is hard to beat. Very natural/uncoloured midrange. Also good bass, but is not very low. You can play loud, but not very loud. (depends on your preference of course). I guess the same goes for the ESL57, but after what I've read, it's even more restricted in bass and SPL. But the purity of the midrange is state of the art.
If you go for a speaker like the Prometheus, you get a speaker with a different presentation. It's extended both in bass and treble. You can play louder. You can use a tube fleaamp. It makes the same disappearing act as the quad's. It's very uncoloured in presentation and has a livefeeling like few other speakers. It's a very good speaker, but it's not a Quad. Both speakers have qualities, and it's a matter of taste and priority more or less. I do not miss my Quad's, cause the bastanis does so many things right and better. But I sometimes wonder how they would sound in my present setup...
As for the Quad 57, after what I've read, it has got some reliability problems in the highvoltage section? The impedance is low at some point, which makes it a bad match with tubes. Don't take this for granted as it's just my subjective impression.
Cheers
Bjorn
