Is not true with my MBP Retina. Facing the computer, the left UEB port did not work and the right did.
Also try to use the cable that came with your AK. When trying to transfer songs directly to the AK, the Kindle USB cord would charge my unit, however the drives wold not be recognized with it.
There is a real difference between the two USB ports. On my MAC (try yours too) go to the Apple logo upper left, click: About This MAC> More Info> System Report>USB........ One is Hi-Speed Bus and the other is SuperSpeed Bus........and get ready for it.................both are USB 3.0.
My right side is what I have been using to connect the Mojo since day one because of positioning. Last week when I tried the the AK for the first time as a USB DAC it was with the left and I could not get it to work no matter what I did. Then, the lightbulb went off, switched to the right port and Violà worked perfect.