X-CANS V-2- Help with tube upgrade questions

I admit I know NOTHING about tubes....I want to upgrade the tubes in my Musical Fidelity X-Cans V2 Headphone amp. I am amazed at the quality of sound this 1 week old unit delivers via my Sennheiser 600's (well, for a headphone rig anyway), but I know the stock tubes are probably pretty cheesy.

Any suggestions from you tube experts out there??

Thank You!
A bigger improvement will be to get either the Musical Fidelity power supply or the Ault high-current outboard power supply from www.hosfelt.com. The Ault will cost less than $20.00 and be a bigger improvement than any tube upgrade. That said, I use the Amperex 6922 gold pin industrial tubes in mine, after having tried several alternatives.
Thanks Viridian! Have you personally used the Hosfelt unit, and if so, can you tell me which one works with the X-Cans V2? I read in Stereophile that Sam Tellig was recommending something like this but some people reported that it destroyed the amp....I want to be sure to buy the one that worked for you!

Thanks Again!
I personally own two of the Ault high-current power supplies and they work really well. I have been using them for over six months now and one of them stays on all of the time (it powers my X-LP in my little bedroom system). I would only add that my X-CANS is a V1. The likelihood of destroying the X-CANS would come from ordering the wrong power supply, AC vs. DC, etc. I am at the office, but will e-mail you directly when I get home with the exact model on the Hosfelt website.