I got my P5's the other day, and I'm noticing that these headphones are not as good as my M50s, I've read on a number of sources that these headphones require extensive burn-in. How long? And what is the perferred method?
A long time since I heard some M50s so cannot recall exactly what they sounded like in comparison to the P5s but enough to say they are approaching music from a different perspective. The P5 is designed to be a warm, friendly to most genres, lightweight portable whereas the M50 is more a studio monitor type IIRC, more like my Shure SRH840s.
While perhaps not audiophile flat, the P5 excels when used in commutes and so on where the extra bass and warmth overcome invading sounds from around you. Their light weight and comfort especially as an on-ear makes them easy to wear for relatively long periods without overheating your ears yet have reasonable isolation. The slightly recessed treble is not tiring at all yet they don't sound dull at all. I like them as travel phones especially since they fold so compactly.
If you want something more neutral then maybe have a listen to some Sennheiser HD25-1 II. I also have these but mostly listen to them at home. Can someone else advise if they are closer to the M50s?
Finally, I don't feel the P5s have altered much with burn-in. I must say though that I notice this less than many others report. I tend to think burn-in is more about growing accustomed to different sounding phones than big changes on the whole. But that's just my view.