Pacific Valve Dac 60...Tubes?

What tubes are they? If you tell those of us who don't know the Pacific Valve DAC 60 like me. We may, still, be able to make some suggestions.

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

Try the JAN Philips NOS. Nice sound for cheap...

I own the non-Pacific Valve modified DAC-60 and replaced the stock Sovtek's shortly after acquiring it. While I noticed better bass response, improved system speed, and gained a fair amount of blackness by going with a DAC, something seemed to be missing. So, I went with a pair of JJ Tesla's from Upscale Audio at $30/each. These tubes were very smooth, airy, and made the Sovtek's seem congested. After reading a few glowing reviews on the Amperex 7308's, I figured that I'd give them a try. Wow! Where the Tesla's left off, the 7308's took them to another level. These are much more detailed and warmer sounding than the Tesla's. While they were $80/ea from Upscale Audio, they were well worth it. much more detailed and warmer sounding than the Tesla's. While they were $80/ea from Upscale Audio, they were well worth it.