If you prefer to keep things simple one possibility would be the Headroom Balanced Desktop w/ the Home/Home module options -> balanced HD600 or 650. I'm pretty sure you could get into that and that it would sound significantly better than your current rig (based on my impression of the ED9s in better rigs).
Otherwise, if you want to keep your components separate there's way to many choices to run through. My only advice would be to budget equal parts for both your source and your amp, going overboard on either one never makes any sense to me. And I tend to spend the least amount of $$ on the headphone part of the equation, there are lots of good headphones under $400 and I have yet to hear twice the performance from the next tier.