I auditioned the X2, he 500 and he 560 and I thought the X2 and he 500 performed very well with the pan am. It was a pretty close call between them but I did prefer the he 500. I did not think the pan am played well with the he 560. Maybe it was the particular pair of he 560s that I had but they sounded thin, very bass shy and seemed underpowered. The pan am should have had enough power took handle them,so I don't know what the story was but they were easily my least favorite out of the three with the pan am. To my ears the x2 was the best bang for your buck out of the 3 though the he 500 is dropping in price and is also an excellent value and better headphone though I wouldn't say drastically so. If you're diligent you can find them new for $500 or less and used for less than $400. X2 can be had used on Amazon for $225.
I agree! In my A B comparisons I thought they were very, very similar in signature and I was surprised by how close the X2 was to the 500 in sound quality and it is definitely more comfortable. . It really is an amazing value.