I love the sound of the X-Can V2 and more so with the Pinkfloyd Mods, I have owned mine since May 2006 and a lot of amps have come and gone since. Many of these amps were far more expensive, yet the X-Can V2 remains.
As far as the Little Pinkie PSU it is expensive and well worth it. However I can understand the reservation on buying it, I will propose a much cheaper alternative ... Jameco sells a 1.5 amp 12 VAC (notice I wrote AC) for under $15. It is better than the 500 mA 12 VAC wallwart that is included by Musical Fidelity.
For a while Sennheiser (EU) demoed their cans (HD580/600/650) with amps by Musical Fidelity which should indicate what they thought of the amp. I do not know what sound card nor the quality of the files you are currently using. I say thus because the amp can only reproduce what is being fed. As an analogy: using top of the line tires designed for a high performance car on an econobox will not allow you to fully experience the abilities of the tire.
I would implement the PinkFloyd mods in the X-Can V2 you have and I would get the Jameco power supply and see what you hear. BTW, the valves in the can may be pass their prime, a pair of matched GE or Sylvania 6922 or Russian 6H23-EB will further improve the sound.
Otherwise shoot me a PM if you want to sell the X-Can V2.
Good luck.
Miguel