I have all three of these, and I'm a real non-fan of the DT231. I find it just plain boring. The bass goes quite deep, and the treble is very extended, which I found a really attractive feature at first -- I put it on and thought, wow, this is really something at this price. But the midrange is very un-alive sounding, at least to my ears. That was unamped. Amping it actually served only to outline more clearly just how blah it sounded, strange though that might seem.
That said, one great thing about it is that when you have the music turned way down, instead of just hearing a murmur, you still get a good sense of the music from the strong bass and treble response. In other words, it's an awfully good "background music" headphone.
As you can see elsewhere in this thread, many others do like this headphone. All I'm saying is that your mileage may vary.
Between the PX100 and the K 26 P, I think both are good. A lot may depend on whether leakage is an important consideration, since the PX100 is very leaky and the K 26 P much less so. I like the PX100 unamped from an iPod quite a lot. Pretty good all-around, with some extra bass emphasis. When amped, it PX100 develops a really excessive bass emphasis that I find unlistenable. It would be unjust to call it boomy, one-note bass, but it does lean in that direction.
The K 26 P is also very good, and has a really fun sound, but is also a little bit closed-sounding, and seems to me a little less tonally accurate than the PX100. Still, I really like it, it's awfully musical, has great bass, and its slight isolation seems like something that would work well in a gaming context.
Both the K 26 P and the PX100 are light enough and comfortable enough for extended gaming sessions. I think the DT231 is much less so. The K 26 P and PX100 have short cords (1.5 meters, I think), while the DT231 has what I think is a 3-meter cord. The K 26 P folds down and has a soft zippered carrying case, the PX100 folds down and has a hard plastic case, and the DT231 doesn't fold and has no supplied carrying case.
For rap music, I think I would recommend the K 26 P of the two: its bass is very present yet nicely controlled, and the overall sound is a little bit on the "phat" side. The DT231, though I don't like it for the kind of music I listen to, is probably a pretty decent rap headphone: the lows sound really good. I have some doubts about the PX100 for rap since its bass is on the boomy side to begin with.
I'm not very sensitive to soundstage, and can't offer you any sort of useful comparison on that score.
