Avatar SE Tubes

Can anyone recommend tubes for the Avatar SE that will increase 3 dimensional sound and possibly slight midrange bloom? It currently has the stock tubes and I'm wondering which direction to go. The stock tubes sound great but you understand...

I'm interested in NOS tubes as well as current models but am looking at spending maybe $300-$400 without phono changes. I'm sure this limits my choices but any advice very welcomed. Which tubes are most important to start with?

Thanks