Say Audiophileboss; I use a Dragonfly with my MacBook Pro to good advantage for a list new of $250. Powered by USB, it includes a 64 position volume control too. Tiny, but very good, it plugs into my Custom Bottlehead Linestage via an Audioquest - Golden Gate Mini-to-RCA 1.5M cable.
http://www.stereophile.com/content/audioquest-dragonfly-usb-da-converter
BTW, Gordon Rankin of Wavelength designed the Dragonfly.
Cheers, Hank in Eugene