My current setup is the Sennheiser Momentum plugged in directly to my 2012 Macbook Air. My music is streamed from Rdio, which I believe uses 192kbps lame-encoded mp3s.
Would my setup benefit significantly from a standalone DAC? If so, which do you recommend for around $150? Preferably, I'd want something that I can conveniently bring to and from work everyday.