Lamm L2 Reference tube recommendation

I feel guilty, I never tried that in my L2R but I am interested in your results

The thing is there is swapping signal tubes and swapping power supply tubes. The LL2 is a tubed pre with a tubed signal path. The L1 and L2 are solid state with tubed power supplies. So in a well designed circuit, there is less of a difference with swapping tubes in the ps.
But in my case with the L1, the difference was easy to identify albeit small.

I dont think you'll find much improvement tube rolling with the L2. The most important thing is to check the voltage output of the power supply as specified in the manual. Slight deviations, usually loss in power will make it sound dark and veiled. Unfortunately I found myself making this adjustment weekly and replacing the tube monthly making it too high maintenance for my taste.