BassInZurich

I just spent a truck load of time checking headphones on my helix, ab'ing with different audio interfaces and different setups. All because I have the same problem as the OP. I reckon some headphones simply sound awful with it. My Audio Technica M50s are really bad and sound just liek OP described, yet my cheaper M30s sound quite nice. upshot is I'm off to buy some new headpones.