The reason Pass Amps don't respond to high-cost power cords like other amps is, and I'm not sure I understand this 100%, but I've read that as true class A (I have Aleph 5 - and this may not apply to their modern Class AB amps) they draw the same current all the time. It either gets used for heat or music, but doesn't change. Amps that operate as Class B will pull more wattage when the music peaks, so all of a suddent asking the wall for 10X the power you were using a microsecond ago, if your power cord is higher end there may be less resistance or capacitance or whatever, and it gets there more quickly and/or in a purer way. But the Pass Class A amps (and I suppose any true Class A amp?) always draw the same amount of current independent of the loudness or local intensity of the music.
So, this would mean, if correct, that the XA200 or XA160 would not require crazy power cord, and your X350 would only to the extent that it was in class B mode. I've read here and there at what wattage it goes from A to B, don't have the info at my figertips, its realitively high for 350, so the only effect you should hear is when you are listenting to very very loud music, the amp is in B mode, and then on top of that, the volume changes very quickly. If you had 150, for example, you would be in B mode more often.
Otherwise, it won't make a differnce.
Not to say I'm against spending $150 or $70 on low/medium-end Kimber power cord or similar equivalent, but I don't think going higher in price buys much for reasons mentioned above.
