Got these today, and have done tests with my Cowon D2 and Zune 30, with these unamped and also with a FiiO E5 amp.
First off, I also have Sennheiser PX100's and MX560's, and these earbuds are a significant improvement from them, right out the box. However, these things really need an amp so the E5 is a requirement. My main comparison is between these and my Sony MDR-V6 studio headphones.
Cowon D2 (with D2+ firmware mod): These buds really shine here, given the excelllent EQ and effects on the D2. But when flat, the bass is definitely lacking. In comparison, my V6's have a deep bass. The PK1's have better highs, however.
Zune 30: I am disappointed with the SQ in these, so far. Even with the E5 amp, the PK1's seem a bit lifeless. The V6's are much better, overall.
I am hoping that this will improve soon, as the PK1's do need a few days of burn-in, and I also have a better amp in flight (this could also be why the Zune seems so lifeless, even with the E5 amp).