I have the previous model the Tube Box SE. I have tried a variety of tubes looking for a good sound.
It came with a pair of Upscale Brimar CV4004 platinum tubes. Great sound, nice and warm, one tube went microphonic and I didnt want to pay $$$ to replace so...
Tried a pair of JAN Sylvania 12ax7wa. $80/pair from tubeworld. Very quiet, clean crisp nice range but a bit shrill on the top with harmonica and other similar instruments maybe more burn in time?
Just got off Ebay a pair of IEC Mullard 7025A for $50. Not so quiet but not noisy, nice warm fuzzy sound, which is great with my blues albums.
Tried some Groove Tubes GT12AX7M from Upscale Audio, platinum grade. These sound great in my Primaluna amp but not so great in the Tube Box just plain.
Just bought off of Audiogon some Tungsram 12ax7 that came from Upscale Audio triple matched platimunm. Waiting to see what these sound like. From Upscales website: Very low noise, very low in microphony, and one of the most beautiful sounding 12AX7's on the planet. Neutral and smooth. Excellent bass, and long life.
My system is Primaluna PL2 w/EL34, Triangle Comete ES speakers, listen mostly to blues vinyl, some rock and folk.