I have a PC only system now with a Benchmark DAC1 and the headphone amp inside is very nice. Not as nice as my Melos SHA-1 headphone amp which is smoother, but I had to do some serious A/B to decide if the Melos was worth keeping (it was.) I'm using a pair of Sennheiser 650s and they are amazing.
However...I would wait for the new Benchmark DAC1 w/ USB(coming out next week, I think) You probably know this but if you use a non USB dac you'll need a proper sound card.
Another (cheaper) way to go would be to buy a cheaper USB dac like a Scott Nixon tube dac (on audiogon now for $275) and then a seperate headphone amp like a Grado RA1 (on audiogon now for 250 used) - I've never heard any of this stuff, though
However...I would wait for the new Benchmark DAC1 w/ USB(coming out next week, I think) You probably know this but if you use a non USB dac you'll need a proper sound card.
Another (cheaper) way to go would be to buy a cheaper USB dac like a Scott Nixon tube dac (on audiogon now for $275) and then a seperate headphone amp like a Grado RA1 (on audiogon now for 250 used) - I've never heard any of this stuff, though