Yes I use a dario Miniwatt tube. It sounds better in every way over the JJ. The soundstage is the biggest improvement. The sound is much wider and deeper with better instrument separation. The mids, highs and bass are better defined as well. I have a 1950's Siemen CCa tube coming soon.
Thanks for the interesting informaton! The Miniwatt tube might be of a great interest to me as soundstage is something I care about. Please let me know about the Siemen's tube when you test it.
Can I ask you how much you paid for your tubes and where you bought them?