Pacific Valve Dac 60...Tubes?

Sorry! Should have mentioned that.
According to the Pacific Valve site they are described as "6922/6DJ8".
This is my first experience with tubes. A bit of research showed there are many 6922's and 6dj8's. How does one know which are better? Also, is there a site that gives a description of the sound characteristics of different tubes and which can be substituted for which?
Thanks
Steve

A little more research shows the tubes to be Sovtek 6922's. Discussion reveals these are about the poorest of the 6922 so I am looking at a pair of Amperex ECC88 Holland A Frame Orange Labels. Just want to dip my toes into tube rolling so these will be used but tested. Any other recommendations would really be appreciated.
Steve

Toufu
Thanks for the suggestion. Hadn't even considered the Jan Philips. Will be keeping an eye out for a pair.

Iggymin
The 7308's are a bit pricey but from what you describe it sounds like a buy it now or buy it later. Might be best to just skip the in between and get close to the top. Will be watching for a pair.
Thanks to you both.
Steve

Bought a used pair of Amperex BB 6dj8. Very nice compared to the Sovtek.
Am still looking for the right tube. System composed of:
Squeezebox Duet
Dac 60
B&K Ref 20
Bryston 3bst
Gallo Ref 3.1
Sound with the bb is very nice on good recordings but on older Rock cd's it is a bit fatiguing. Seems I may need a little warmer sounding tube. Any suggestions?
Am looking at a pair of Amperex USA PQ 6922 but they may be out of my price range.
Thanks for any suggestions.
Steve

Stivervii
Thanks for the list. Just bought a pair of Amperex Orange Globe. Anxious for them to arrive.
Steve