Anyone swapped out the stock JJs for something better? Maybe Tung-Sol or Electro-Harmonix?

Thank you for the link....very good info. in there. Do you think there's a benefit to changing the power tubes?

Oh contraire... There is no bias adjustment for the 12AX7 pre-amp tubes. They is what they is.

The biasing is required when replacing output tubes only (the 6L6's).

The Tung Sol 12AX7s are very gainy (too much for some situations, IMO). They sound pretty good, but I have had several go bad prematurely (after a few months),. Not Good. I also have a lot of experience with Sovtek, Groove Tube, EH, misc chinese 12AX7s, etc. I have some NOS Mullards, RCA Phillips, and a few others, as well. After all this experimentation, I have come to the conclusion that the JJ 12AX7s are the most consistent for good tone and reliability. I buy my tubes from Bob at Eurotubes. He hand selects his tubes for different applications and sells them that way, and I can tell you that the use of these specially picked tubes  really makes a difference.  Especially for the PI tube.

BTW I have had Sovtek 12AX7s, EL34s, 6L6s and have been disappointed with all of them. The reviews on Sovtek 5881s are not very good  either, notwithstanding the fact Larry Carlton makes them sound pretty good to my ears.