So are you happy with the 6T9? Have you tried to improve the circuit at all? Since those Edcor transformers have UL taps, perhaps you can try and see if you prefer that.
I'm extremely happy with the 6T9 amp using the Spare Time Gizmo brds. There are a couple of areas where the cct. can be improved:
Use the Edcor trannies and the UL tap. You can solder the UL tap direct to pin 10 which is the screen grid and leave out or cut away the 1K resistor easy.
Upgrade the coupling and input caps to .22uf. This improves bass. Use a good quality metalized polypropylene as a minimum. I use inexpensive polycaps and they sound great. Space is limited where the caps mount but don't let this stop you.
Double the last PS cap from 100uf to 200uf and snub both PS caps (.1uf) and snub the diodes (.01uf).The snubbers for the diodes will drop into the same holes on the PCB - too easy. The extra PS cap improves bass dramatically.
I went over-rated with the power tranny (Hammond) and the Edcor OPTs are rated 15W. The amp produces 4.5W!! I also rubber mount all trannies. Keep the signal earth and mains earth separate. I only used silver based solder (5%). The amp is dead quiet. No hum or hiss-nothing.
The amp has a massive sound stage and very detailed. Extremely musical I would recommend the Fostex FE167E drivers (Gio's suggestion which I followed) to go with the amp.The combo of the 6T9 and Fostex is made in musical heaven and produces one hell of a sound!!