I find the NOS Sylvania 12ax7 and Baldwin 12ax7's work very good in the modules. they are clear, articulate, high gain and low noise. they are fairly cheap too.
If you want cleaner "cleans" then try the 12at7 > 12ax7 or dual 12at7's
again, sylvania's work great in the 12at7 range. 12at7 has...