I'm rookie among the tubes, so take my view with a grain of salt, but this is the way what I try to follow:
I don't want to spend hundreds of dollars into different tubes, but try for the best possible few tubes what my budget allows. I know, many NOS tubes are fantastic, but I don't have the knowledge to decide which offer is good and which one could be a scam.
Therefore I decided to buy NEW tubes in the first round.
As far as I know, driver tubes have bigger role in the sound signature. I already have a NEW TUNG-SOL 6SNGTB as a spare tube. As my money is not unlimited, after a few days of web-search I pulled the trigger on a Chinese tube with very good reputation. This is the Shuguang CV181-Z, aka "black treasure".
https://www.tnt-audio.com/accessories/shuguang_treasures_cv181_e.html
It requires a good amount of burn-in time -30-50 hours- but the general consensus is very good. I'll test it and decide between the possible power tubes according to the signature of the Black treasure. Some people says the Psvane tubes are better, but this is not a common consideration, and the appropriate Psvanes are slightly more expensive.
If you strictly want to fit into your budget with the two tubes, the Russian TUNG-SOL 6SN7GTB is a class above the stock driver tube, but beware: it hums -at least with my DV336SE-, but I will do the fitz mod next week.
I hope, somebody can advice a nice, budget friendly power tube for your system.