I just changed out the stock tube with "Gold Lion" E88CC. A nice bump up in the sonics. Cleaner, clearer, richer, more transparent even before they warmed up. Impressive. An already great product takes a step up. Way more than I expected, if I expected anything, skeptic that I am.
I went for all the alternatives they offer, triode, high gain,balanced, low noise and microphonics. I really don't know what most of that means, but it sounded good, and didn't add that much to the basic cost. Maybe Morten can offer some comments.