Is anyone running Amazon Music HD or Ultra HD with the Air and if so, how?

BTW, Ultra HD is supported at 24-bit, 192KHz for "millions" of songs. You can't get any better than that provided you have "good" equipment that doesn't introduce inter-modulation distortion. HD is supported for 50 million+ songs at 16-bit, 48KHz which for the vast majority of us, is more than perfect.