My grandfather just purchased himself a very nice pair of headphones, the Beyerdynamic Tesla DT 1350
He is currently using them on his Macbook Pro retina. He listens to good high quality music, and I feel he is greatly limited by the sound card in the mac. I am asking, what is a good, mid priced amp, probably USB, that is mac compatible?
I found the Audioengine D1-
Would that be any good? Any others you would recommend?