I don't think anyone is recommending the P7 as the ultimate reference headphone, that would be silly. The P7 is a very good portable headphone that sounds good enough for many people to also be their only headphone. There are cheaper headphones like the HD600 that sound better, but obviously aren't portable. There are cheaper headphones that are more portable but don't sound as good. If I needed mobility and could only arrod one pair of headphones then I would recommend the P7, and then add better cans later on for home use.
My point is, while they're not ultimately reference headphones, the P7 are good enough to be an all-rounder.
As far as amps, we'll have to just disagree there, I found that the P7 responded VERY well when I added the Theorem 720 into the mix vs using just the iPod.
I had the P7 with the Theorem 720. I thought it wasn't a big improvement. It was clearer and bit more refined sounding over all but definitely not a big difference.