Well, I just recently got the Tung-Sol 6sn7 "mouse ears" tube. The soundstage feels vaster and the bass more present than the electro-harmonix 6922 tube I previously favored, so no regrets on leaping on it. If bass and stage depth is your goal, a tube like that might be a step in the right direction. Also, if you don't have a vendetta against equilization or sound processing, I highly recommend trying OOYH (Out of Your Head) software for a better soundstage presentation and bass emphasis (this greatly depends on the chosen effect, the Ultima preset scratches both itches for me). I found that it does require some EQing to properly tune it to your headphone though, but the results when done right speak for themselves.