Jadis JA30 - Quad ESL63 .. 4,8 or 16ohms?

4est, you are discussinging the Quad ESL63 with the same ideas that are usually applied to electrostatics such as SoundLab and Martin Logan, but the ESL 63 is a different case. SoundLab and MartinLogan have impedances that can be as low as 1 ohm, but the ESL63 never goes lower than 4 ohm, being 5 ohm at 10kHz. Unless you listen to a lot of heavy rock and electronic music the power of music at frequencies above 5 kHz is much lower than average power - I have measured it with a spectrometer. Some versions of Shostakovich symphonies or some challenging test disks have peaks that are exceptionally rich in high frequencies, but most of the music some one typically listens in ELS63 is not a problem. Remember Peter Walker designed the ESL63 for the Quad 405 that was also current limited.
May be you prefer the 4 ohm tap because with this tap the damping factor of the amplifier is more adequate for your taste and listening environment.
I did some research and plenty of measurements on electrostatics because I own an amplifier that sounds lovely with electrostatics but it is current limited - the Dartzeel.
If someone has interest in the original HifiNews 1981 measurements I will be pleased to email them.

why not just try for yourself and hear the difference

4 ohms will have a tighter but somewhat dryer sound

Because it's useful , if not necessary , to listen and compare your experiences .. Philijolet

Just to chime in with my two cents, my ears always preferred the 8ohm taps with my Jadis amps driving the ESL63s: Sweet highs, good warmth, not exaggerated and a decent bottom. 4ohms made bad CD's sound even more awful and I did not like the high end with 16ohms, if I recall right.

Thanks Detlof .. what you wrote is the exact result my friend is getting with 4ohms JA30 setup
I think too the 8ohms setting is the best because stays in the middle .. pratically he won't lose the grip on the low frequencies and won't lose the highs presence