Connecting MacBook Air to DAC

USB should work fine… I used that for years.

uSB but may have to upgrade OS to latest if the usb audio device does not work. I had that happen just last week. I found the upgrade solution for the issue with a simple google search and that resolved it for me as well. If you are on latest OS version already should be fine. 

It's the day for Mac!  USB will be fine, but you may have to adjust your Audio MIDI settings (in Utilities) to get the bit rate and speed you want for your files.  The Mac will up-convert, but it doesn't do a really great job.  Better if you match the MIDI to the files you're playing.

Have fun and happy listening!

If you use Macbook, then you should try out bit perfect app, it will make a significant difference in your sound quality coming from itune

I second BitPerfect ($10). Made for a clear improvement in my system