They run KT88. EL84s and 6922. 87% efficient. They can run out of gas with a low efficiency speakers with yours at 90% they should play just fine. UL. If you can use 8 ohms valves will like it a lot better. Loose the bass duty it will be a one up, again.
Tubes amps don't do really well trying to control larger VC drivers. 4 ohms is even worse. KT88s will take up a little slack though.. Learn to bias correctly.. Best thing you can learn right now... UL, bias cool, try 8 ohms, loose the bass.. :-) Cary is fun.
I'm looking for another V12R (Red). I have a pair of SixPacs too. 6V6, 6L6, KT66, 6550, EL34, KT77, KT88, KT90, KT99 all work in both units. The V12 will work with 4, 8 or 12 valves. They work very well from 17 wpc to over 100 wpc. Great amps..
Regard