Quad ESL-63 and low-powered amps; Sun Audio, Atma

+1 I own their later incarnation, the 2805, after having owned the original ELS57 for many years. The 2805 (and 63) has a pretty low sensitivity (lower than the ELS57). Originaly I drove my 2805’s with my old 2x45 watt Quad 303 power amp, but that was not enough (we had also moved to a bigger house). So I bought a refurbished 2x140 watt Quad 606-2 (the almost identical equivalent of the more recent Quad 909, QSP and Artera amps). That was clearly better for more dynamic music. Even so, I can still hear limitations, and consultation with Quad UK’s Rob Flain suggested that in our large room the 2x260 watt monoblocks would be an improvement. This is just to give you an idea of the ballpark you should be considering. And of course, Quad’s own current dumping amplifiers like my 606-2 or its later incarnations work well with the speakers - and for a quite modest outlay. It was not for nothing that around the time of the introduction of the ELS 63 Quad came out with their 2x100 watt 405 current dumping amplifier.

Funny to see this old thread reactivated! I started it back in 2015. Lots of equipment under the bridge since then and I thought I would share my experiences.

Roberjerman is right... Single ended amps just didn't work with esl-63s. Usually dead on top. Other amps didn't work, such as Shindo, because they are made for 16 ohm loads and anything under 8 ohms is a real problem. The Quads literally blew amp resistors. However the sound was as good as I have ever had... stunningly beautiful, textured, real. Made most recordings sound like music.  It was a 30-watt Montrachet. 
Regarding power, I found even 30 watts can make great music, though be aware that I use Vandersteen 2wq subs so the bass dynamics were taken care of. Still, depending on your Sonic priorities, big power is not necessary. I also used VTL MB-185s on the Quads and they sounded absolutely amazing. The power does bring the macrodynamics to life in a very noticeable way. If your priority is mid-range musicality and timbre and texture, power is less important. If you need great dynamics, then more power. But if macrodynamics are and/or bass are really that critical to you, maybe Quads are not the speaker for you. Even with big power esl-63s are no match for many dynamic speakers, in terms of macrodynamics.
I never thought I would sell my Quads but I did. I compared them head to head with a fully refurbished set of Snell Type A and preferred the Snell's. Now I run a VAC Renaissance 30/30 with the snells and Vandy 2wq's and the sound is the best I have had. But nothing does graceful treble like the esl-63s... I miss that!
 

willemj, is it just me, or are you changing your opinion in regard to amps as you gain experience. If my memory serves me correctly you were stating in the past that all amps sound the same at matched level. However, here you are discussing different amps and sonic changes; I presume without level matching. So, are you forming new opinions about amps in systems? 

BTW, stats are great! I have the Kingsound King III electrostatic and find that power cords make a substantial difference in the performance of the speaker. Don't scoff; try two or three different ones with various geometries and AWG. You'll thank me later.  :) 

No, that is a misrepresenttaion of my position. What I said earlier was that they should be judged within their design parameters. So as long as a well designed amplifier is not driven into clipping it should sound the same as another one not driven into clipping. However, elsewhere I have also argued that you need a lot of amplifier power to avoid such clipping of dynamic passages. And that is precisely what I think was happening with my poor little 303. So again, I don't doubt people hear differences, but it is important to investigate what it is that they are hearing. Beyond insufficient output power, there may also be issues with input clipping due to a gain mismatch at the input stage, or a load dependent frequency response. But those are different issues that I already discussed earlier. So my position is a bit more complex than you may have thought.
As for my experience, well I am not a novice, not at all.

I had great success using 60-70 watt ARC tube amps when I ran Quad 63s (mine were Crosby modified). I went from the 57, which was augmented with a sub and ribbon tweeters and found the 63 (without the need to supplement) to be the better all around speaker, but it lacked the "magic" of the original 57. Guess which speaker I kept, had restored and still use (in my second system)?