I'm not sure but shall try.
Reasonably strong bass, but not bloated or overpowering the mids.
Not too warm, basically I'd love the H6's (same goes for the AKG 550's) to have more bass or the P5 / XS to have more detail.
Out of them all I'd say the H6's edge it for me as the detail they give vocals in particular really appeals, it's just there are times when I'd like them to have a touch more bass.
I can't speak to any of the headphones you have except the (original) B&W P5's. The M2's are not perfect out of the box, but I totally agree with
Giogio, in that a good pair of headphones may not be perfect for you out of the box, but can be eq'ed to perfection. Not all are capable of this. For instance, the P5's will NEVER have much detail, no matter how much eq you give it.
That being said, the M2's can be made so sound absolutely fantastic (especially compared to the P5). The bass is more accurate, mids are a little forward for my tastes, but that leaves room to eq the bass and treble, and not make them too recessed that you can't hear them. As for treble, they have the Senn veil. The good news is that you can add TONS of treble to them and they never get sibilant. Adding this treble also helps the lows sound better, as it helps with the overall tone. So now, you can have some thump, AND accuracy.
To give you an idea of my tastes, I find the bass on the P5 to be bloated and not very accurate at all (though enjoyable for some moods). The M2 are also bloated somewhat (in wired mode), but not overly so, and DO have some accuracy to them (out of the box). This will also depend on your source files, and DAP.
If you are using the standard iPhone or iPod, you will find the M2 to be warm-ish, whereas you might find using something like the Fiio X5 to be more open. For myself, I enjoy (as my portable rig for these phones, and wired): Fiio X5>Fiio E17K (The nature of the E17K is sharp which is what I want for these headphones)>M2. I have eq off in the X5, and have the E17K set to +6 on treble (out of +10). If you want to rattle your brain, you can go up to about +6 on bass, and the M2 scales decently. Otherwise, these have enough bass for me most of the time to not need any boost.
Keep in mind, that the M2 are NOT perfect, and you will NEVER reach the revealing nature, or airyness, or soundstage of something like my HD700's, but I would say that you can get a very fun sound with these. I have been in love with these since I got them, and if you use these with BT, I find them to have absolutely gorgeous sound without needing anything really.