I've tried the 6H30 and the Genalex 6922 tubes in the Tube Buffer. In my system, the 6H30 was more neutral and "disappearing". As Morten said, the 6922 sounded more lush, but in my system and to my ears they strayed enough from a "straight wire with(out) gain" that they left their fingerprints on the music. It is great though, to be able to plug and play with a variety of tubes. By the way, Tube Buffer with the 6H30 has tremendous, tight bass extension.