Just picked these up on my way to work (thank you 24-hour Apple Store 5th Av!). Here are my initial impressions (they are currently in the process of being burned in at my office):
First off, I had forgotten how God awful the music loaded on to those display iPods and iPhones were. I initially tried the P5s out listening to the stuff that they had loaded up on a iPhone demo unit. The first thing that popped into my mind was "Wow, these P5s are pretty lousy, I get better sound from these super cheap and not very good Klipsch S2s!" Then it occurred to me that it might just be what was on the iPhone demo unit. So I unplugged it from the demo and plugged them into my own iPhone. Remarkable difference! So there you have it ladies and gentlemen, the music loaded up on the iPhone and iPod demo units are horrible and nothing will make them sound good.
Secondly, these things grip your head like a vice, the good thing is that the padding is very soft and pillow-like thus they are not uncomfortable. I can't imagine my ears getting too hot with these on either since they don't really make all that much contact with your ear. Most of the sealing I feel is around the ear canal but it's a far cry from having your entire ear area flat against let's say, a pillow. I don't see a foreseeable problem with the fit or excess accumulation of heat on ones ears with these things.
Now, on to the my initial impression of the sound. My expectation going in was of something that sounded pretty much flat with no part of the spectrum being outstanding. I was expecting something along the lines of a mid-range pair of UEs. Thankfully this is not the case here BUT my expectation going in IS partially correct. There's no particular part of the spectrum STANDING OUT better than the rest of the spectrum but by no means are they flat, the P5s are just not really particularly coloured or really have a "unique sound signature" apart from them having the sound which is equivalent to listening to something that is totally not under the influence of any external EQing apart from how the track was originally mixed.
Another thing to take note about the sound is that the P5s is most probably best described as "intimate" in regards to the soundstage. You're not going to get that stadium or orchestra sensation when listening to the P5s. What you will get however is the perception of having the singer and instruments in the room there with you (and not a big room either, think recording studio sized room).
These are all initial impressions of course as these are still being burned in, but there you have it, relatively good initial feelings towards the P5s. My gut tells me that they are going to be keepers. Also of note, these definitely are very well made, packaging is gorgeous and I love the tray that the headphone comes in (it's covered in what seems to be stretchy speaker cover material). Portability is definitely the best in class I would say (I'm amazed that these are 40mm drivers since these things are pretty darn miniscule).
