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!
danlib1
Post removed 
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!
Post removed