Oh, do try some other tubes than the EH and Sovteks! They are "adequate", IME, but certainly nothing special. I have had great success trying 5751's in place of 12AX7's at the driver station for an EAR 890, and there are great options for voicing the amp in a direction you desire, all of which are definitely superior to your current tubes for musical finesse. I like RCA 5751 Triple Mica Black Plates when I want a richer presentation, a "warmer" influence, as it were. If you want a more articulate (but potentially leaner) presentation, try a GE 5751 Triple Mica Black Plate. Now, when you want the best all around performer, IME, try a Sylvania 5751 Triple Mica Black Plate. That is where I settled, but each amp, system, person is different....
Also, Joe's Tube Lore is definitely worth a read through over at AudioAsylum (in their FAQ's section for tubes).
Also, Joe's Tube Lore is definitely worth a read through over at AudioAsylum (in their FAQ's section for tubes).