If I can find it, I've got a photcopy of the "Amplifier Circuits for the KT88" GEC application note which has several circuits up to a 400W parallel push pull monster. 6SN7s figure, ISTR. I copied the note from the Tech Library at Racal in the 70's when I came across a couple of lovely H/B 30W UL KT88 amps complete with Quad 22 preamp and some large, knackered, Heathkit speakers which were given to the local operatic society where I crewed. As luck would have it, after a chance meeting with the former stage manager I found they were still there some 25 years later, and yes, I COULD have them
I'll have a look tonight.....
Chris