Tube info

I’m running the M-125 monos and the gold lion kt88’s made them come alive.

Are you running GL’s in the driver stage also?

You should check out Brent Jessee Recording,  great source of NOS and he has some real sleepers that won't break the bank.   I got some really good early 60s RCA 12ax7 and Philips Miniwatt 6922 and they were everything he said they would be .   His website is a great source of historical info on NOS.  

Jim McShane is a good source too,  nothing but positive comments about his restoration services and tubes on every audio forum.   I haven' t used au7s in a long time but stay away from the later production sylvania nos... mazda cifte 12au7 that I tried other than modern production and they were great. 

There are more parts than tubes in an amp that affect sound. I have replaced noisy metal film resistors in $12,000 amps that had gone high resistance and very noisy.
Replaced them with wirewound resistors for better than original sound.
Of course coupling caps have been a target for replacement and should be explored. Power supply caps also has an effect.
The emission and gain characteristics from tubes is very voltage dependant. You could tweak the filament voltage a bit up or down, maybe 10 or 20% to see what effect it will have.

Jim McShane is my source .  He tests and tests and is very picky.  He will not sell you tubes without knowing what amp they are going into. 
@ Broussard that must be some private collection ! I consider mine large but don't have inventory like that. Well not as organized anyway.Yes Gl tubes can transform an amp I know, also the GL -KT-88s made a huge difference.  Good Luck