Well, it's not much feedback really and I'm not up to reviewing tubes tbh.
Driver tube rolling on an amp gives more than subtle changes but they aren't world shocking either.
From the tubes I have (main tubes are 6SU7GTY BGRP and ECC35 short brown, different versions) the Sophia is the cleanest, more modern sounding tube. See, that's why I hate putting labels on tubes and other gear: it doesn't mean the other tubes are muddy or not clean enough and it doesn't mean the Sophia is bright either. But there is a difference and I can hear it even though I can't instantly A/B the tubes and I have to turn off the amp and switch the tubes. I don't wait for cooloff however, I switch 'em hot with a glove.
I would choose no other than grade A for two reasons:
1 - A Zana deserves the best. It'd be silly to spend 2.5k on an amp and then save $100 or so on a tube.
2 - How would one evaluate the SQ of a tube when not getting the best version of it?
Apart from that, if you don't like the tube it will be easier to sell grade A than lower grades I can imagine.
And what's more, that tube looks awesome on the ZDS with the bigger oil caps.
It's nearly as tall as the power tubes, a difference of 1.5cm I think.
All in all well worth a try, I'd recommend giving the Sophia at least a try to every Zana owner.