If you are going to use the MacBook pro to a DAC via USB get yourself galvanic isolation. Most good DACs now have a decent clock for asynchronous transfer, so you are OK there, but the noise from the Mac is a real issue. I bought an Intona isolation device and heard a big difference - no AB testing required. Also, and this surprised me, switching from a cheap USB cable mattered. The isolation device helped even with a Qutest DAC, which is supposed to have built in galvanic isolation. Also, getting shielded power cords near the DAC made a difference.
