I received my pair of copper coloured M5's today and couldn't quite believe my ears after reading the reviews. Mine sound really veiled as well, with their greatest weakness being the reproduction of snare drums. I've tried with some electronic and drum 'n bass tracks at first and found that they had really good bass extension, even into sub-bass levels, the bass being strong but not extreme, but as soon as I tried some Vocal and Rock tracks it occured to me that there must be something wrong with them. I have never heard drums sound so tinny with any headphone, ever. I have tried almost all of the tips, and can get a decent seal with half of them, but the quality of the sound barely changes. Unfortunately, the reason why I know I'm getting a good seal is driver flex. I had this issue with my Meelec M9s before and these 'phones have it, too, despite many reviewers saying that theirs do not. I will contact MP4nation about this and point them to this thread, hopefully they can do something about it. They weren't expensive but I was expecting at least a slight upgrade from my M9s. The only thing that these do better is sub-bass, the rest is just compressed sound in a tin can. No soundstage at all, voices are veiled, mids are muddy, and drums sound terrible.
PS: I am burning them in with my iPod on shuffle at the moment but I don't really expect them to change much, because I don't really believe in burn-in and it has never really affected any of my headphones in the past.
i would recommend check speaker polarity issue.
i had some unit out of phase issue on brainwavz m4 and beta.