I got the MA750 a couple of days ago and I think we must be listening to two very different IEMs. The ones I'm listening to don't have a small sound stage at all, with good imaging and instrument separation. The treble is clear and detailed but not overly so and if there is any roll off its very agreeable to these ears - don't forget, I'm an HD650 aficionado. The mids are slightly warm if anything, though they are still full of detail. The bass doesn't seem rolled at all to me, it's just not boosted, though it extends well into the sub-bass. Overall I find the sound quite natural and not tuned for fun like the rest of their range.
The MA750 really doesn't like low bit rate MP3s, they sound pretty bad, so they are living on a diet of 24/96 FLACs and loving it.
I agree that they are heavy but when you loop them over your ears that becomes something of a non problem. I appear to be lucky with the fit, I'm using the largest tips and they are just the right size for a snug fit without being overly tight and are comfortable for long listening sessions. Saying that, the outside of my left ear is a bit sore but I did have them in for about eight hours straight yesterday.
I did try the Dunu DN1000 and while they are a very impressive sounding IEM the treble is a bit hot for my ears and left me wincing a few times. As I mentioned above, I'm an HD650 aficionado and heavily EQ my K702s - extra hot highs are not something I enjoy.