Can anyone reccomend a portable DAC to use with my macbook pro and B & W MM1 speakers. I travel alot to my ship where ever she may be and I use my macbook pro for listening to music and watching movies. I'm looking for a DAC that will work well with my speakers and headphones. Any suggestions will be greatly appreciated.

On the go system: macbook pro 15" 500GB SSI drive, i7 dual core processor, B & W MM1 speakers, Grado PS500 headphones, Audivarna plus.