I've been a stat fan for nearly 40 years. I find the pairing of electrostats and tubes to be magic. Electrostats are typically 91-92dB efficient, so you don't need a ton of power. You should have plenty and those VTAs are sweet.
I'm not a fan of the ML ESL9, but the 13a and 15a, I like a lot. Mating your excellent amps with the ESL9 is like putting a Ferrari engine in a Chevy Malibu.
Good luck.