quite a bit of burn in, so I gave them more time. So a few days later I tried them back on. I liked them more this time and really liked the construction and the fit/comfort. After reading the burn in comment, I left them playing radio for about 8 hours overnight one night. I have been using them almost exclusively at work since then and I am really starting to appreciate them.
I am a little confused by your experience with the MM400. I found them VERY bassy (I'm a bass player and drummer as well as engineer producer - 30 years) and I found them bass heavy right out the box. I DID love the sound though - it's anything but flat - very hifi - (mids recessed) but they are sort of like a loveable big floppy dog.
The bass is not what is fed into them - it is pushed. The mids are pulled back a little bit. The highs are just delightful not analytical but detailed and sitting back so not to get on you nerves.
The MM400 is one word - SMOOTH.
I like to use the MM400 for any relaxed music. They are so lazy in their delivery I find it utterly charming. They are like thick honey compared to ultra-runny (yes, viscosity fluids in sounds) sugar water of many other overly-detailed (thus annoying) headphones.
There must be something wrong with yours.
Please note this... the headphone in socket is not the best made and as you plug it in (with them on your ears) you can have all kinds of stereo experiences. I wondered why they suddenly sounded like crap the other day... It was still stereo, but not right at all... Just 1mmm more push in of the plug - BLAM! there's the MM400. So make sure - it does click a little bit when you get it seated - this is not with their awful lead though. - see a few posts back for a serviceable or good one that will fit (ordinary leads don't). The input socket seems badly made and unless your input plug is correctly seated you will be hearing a small stereo soundstage, bass cancelling out and mids (lots of differences) there quite a lot. It just a slight signal from left channel leaking to the right channel and vice versa.
I think you must be hearing them that way. Twiddle the lead (cable) and you SHOULD find an AWESOME headphone suddenly appear. One FAR better than anything you mentioned in your post, even the P7 (hmm debatable about the P7).
I say push the plug it in a bit more... OR you might need to pull it out a bit more, which I just found out by trying that.
You might have a dodgy cable (the supplied one is plain awful, too thin and very breakable) so you might not have even heard them correctly yet. What you say sounds nothing like the experience of the rest of us who own them, not even close. It sounds exactly like what I hear with the plug not seated in the earphone correctly.
I rate these way above the Momentum (any version), the PSB M4U2, the Beyer T51p, and just about anything in this price range of £200 to £300, IF you want a relaxed super-enjoyable, smiling hifi listen, not an accurate flat one, these are the best for up to $500 or where the Shure 1540 arrives.
Please try some things and get back to this forum because this sounds like a rotten introduction to a superb headphone. I would say IDEAL for Country And Western music (though personally I don't refer to C&W as music - more a dimwitted annoyance - but it sells millions, enjoyed by millions (mostly owning a gun) so who gives a toss what I think). Anyway I'd say MM400 excellent for that of you like it, and excellent for jazz trio stuff. For electronic (dubstep etc) you'll be missing out - the headhone is too smooth and relaxed, same for all EDM. Pop - yes, passably good for that.
Let us know how things progress because I am convinced you have a faulty headphone or a bad cable, or a bad input socket.
