When you stack the quads, how do you wire them?
The reason I ask is I have heard a setup with three '57's per side all wired in series work amazingly well with a ~12W amp. It wasn't one specific 12W amp either, I have herd the Radio Crafstsman C-500, a Beam Echo, a Leak and a PP300B.
Of course all the amps were push pull but the Leak and the Beam Echo were pentodes. When wired as pentodes they didn't cut it however cutting the power in half by triode wiring them brought them into the same power range and sonic signature of the other two triode amps. Reducing the feedback made it a horse race.
The interesting thing is for a single panel per side the "12W PP triode amp" didn't have a shot and the 30W of pentode power was required and ultimately the dynamics never showed up.
dave