Seeking advise on 6922 tubes for a preamplifier..

One thing to remember is that you can gain more or less benefit from a tube depending on their position. You might not need to replace all the tubes to get improvements. The amount of gain you need from a tube also influences how much risk you will take buying off Ebay. When I use tubes in my line stage, I only need 3 or 9 db. of gain, so I've been able to use almost everything I've bought over the years in that position. The phono circuit is a different matter, much tougher to get low noise in those positions. I've had quite good luck buying from sellers on Ebay, very few times have I been burned. The main thing to learn is how to recognize fakes and misrepresentations. The more desirable the tube the more likely to be faked.