Originally Posted by Sherwood
A dac/amp is probably a better investment than any of the above. I'd rather listen to the SR-60s out of, say, an Audio-GD compass than the RS-2 out of a soundcard.
This is arguably the best advice. If you get the compass, it has been said to be able to drive the K701 and HD650 to a pretty nice level, so it has power to scale with you for a couple more sets of phones (given you do not make a big jump). Plus, Grados are not that hard to drive, so to just amp something would be rather stupid, as it will provide minimal improvement (and draw attention to source deficiencies). I would see about getting a Compass for around $350 with the sale right now, and then maybe a $150 ish pair of headphones. Used, perhaps? That way, you get the amp to scale, the DAC, and, if you are patient and shop diligently, a pair of headphones that probably retails for about $200-250.