The acoustats will sound best with tubes that can deliver a good amount of current. That said I’d also pick an EL34 amp over a KT88 amp for electrostats given the sonic signature and midrange magic. Unfortunately EL34 are lower powered, so if you have a larger room you will benefit from EL34 monoblocks. Or an integrated or separate amp using at 4-8 EL34 tubes (4 should be fine for a small/mid room, 8 will be needed for a larger room).

I’ve heard the Pass 150 and I wouldn’t pair it with the acoustats as it has a less warm, and thinner character compared to much of Pass’ other offerings.