I’ve been meaning to add my .02 here for a few days, but have been busy.
I’m sure that many of the recommendations above will sound good. The OTL amps, in particular, will have a certain magic. I auditioned a pair of well-regarded Futtermans and thought they were great. But I was put off by the potential hassle of re-tubing those amps.
I also owned, and really loved, a Sanders Innersound Electrostatic amp. This was a circa ~2000 version of his current Magtech amp. It sounded awesome.
However, I caution folks about using a Sanders amp with any Quad ESL which has the "crowbar" protection circuit. The protection circuit is basically a dead short. It results in the amplifier dumping its prodigious power into the dead short in an instant, which basically can destroy the amp. Ask me how I know. This requires sending the amp to Coda for repair and service.
My very strong recommendation is to use one of the Quad amps - I’m now using a 909 and am very satisfied. It’s the only amp in the world designed to work with the protection circuit. It isn’t flashy. Not expensive. But an extremely fine all-rounder. Won’t have the transparency of the OTL amps, but substitutes rock solid reliability for that last little tiny bit of detail. That tradeoff is worth it, in my book.