Next headphones? k702 or kns 6400 or something else entirely?

Hello, I just recently picked up a pair of AKG 240s and have so far been very pleased. I enjoy the comfort and sound of the headphones. They're much more comfortable than my old MDR-V700's and sound better as well. I listen to mostly classical and folk. Bass is fairly impressive on some songs, mostly those by The Chieftains. And I appreciate the new level of detail (can be irritating sometimes too, people coughing in the background of classical recordings, etc.), though they don't play as loudly as the Sonys. I use mostly my old iPod touch 2g as a source (I know, a sin). To be fair, it plays as loudly as I'm comfortable with anyways. Now I'd like to try something with a slightly larger driver and flatter frequency response.

I've heard the 6400 at Guitar Center. I think I tried the finale of Tchaikovsky's 4th. It sounded very good and played quite a bit louder than the K240s at the same volume. The sensitivity is higher, though it probably had mostly to do with the much lower impedance. I also like that the phones are light and being closed they would probably travel well. I'm told they look goofy, but I've got a big wonky head anyways.

I'm also interested in the k702's. I like the suspension type headband which has already proven to be very comfortable. Build quality also seems good. The open back design seems to make a lot of sense to me, like an open baffle speaker except reflections are less of an issue. They also have higher sensitivity than the 240s, but also higher impedance. I think this might balance out. My guess is that they would play around the same volume. Also is damping factor something I need to think about? Then the 702's might sound a little better yet play a bit quieter?

I'm mostly interested in sound quality and comfort. Volume is secondary. I'm not sure I want to bother with an amp, I like to walk around the house listening to music with the iPod in my pocket. I think that for me getting too far away from that might be over-complicating it and squeezing some of the enjoyment from it. That said I've also looked at the DT 880 and 770 but I dislike the fact that I'd have to immediately take it apart and change the cord to a shorter one.