Roger Modjeski used the QUAD as his load when designing that amp.
We still use a Quad 57 in the shop today when we test amps we build or repair. If the 57s in question have the Zener clamp boards (an upgrade as they were not supplied at the factory with them) this prevents any over voltage condition within the panels and stops stator-to-stator arcing. So you will have more amplifier options at your disposal.
He has offered in in two versions: as a 35/35w Class-A/B, and as a 25/25w Class-A.What might be one of the best kept secrets is the original RM-10s ran up to 15 watts in Class A and if you light load them you pretty nearly had a Class A amplifier.
I run my 57s with either the RM-10 or Atma-Sphere M-60s, but just picked up a Harvard H3 (Futterman) that Roger Modjeski and I will restore so it will be interesting to here this amp on the 57s when we are done.