I'm opting to get a decent amp for HD 650s. I'm currently using Essence STX sound card which is surprisingly good as an amp but I'm looking for an upgrade. Budget is $700ish and current prospects are Burson Audio HA-160, Musical Fidelity M1 and Graham Slee Solo Ultra-Linear. This would be my first dedicated amp and the Essence STX would serve as a DAC. Main favouritisms include ambient, electro and rock but I consume a lot of other genres. Any suggestions?