I really have to agree with chicolom.
It's hard to give you a solid recommendation if you don't have a lot of other headphone experience to go off of. I.e. you can't say I really like the bass of headphone "X" but want the treble of headphone "Y". However, I'd speculate you'd want a headphone that had a more solid lower end and gives you more bass. Most people that are just getting into headphones want a better bass impact than a more refined treble region. Changing amplifiers isn't necessarily going to give your headphones a big bass kick.
Are you running the STX stock? Can you plug the headphones into something else like an ipod or a phone and see if they overall sound the same?
I don't like headphones that are really bassy. When I say the Q701s have no bass I mean that the bass is very low compared the the K271 MKIIs. I tried listening to the Q701s with my iphone and it's the pretty much the same. Yes the STX gives the Q701 a fuller sound, but in general the mids sounded dull and the treble was really ear piercing. Is the STX really that great of a soundcard?