I hadn't used the RR2150's DAC in quite a while, so I went back and experimented a bit.

The RR2150 DAC does an acceptable job in faithfully representing music. It's certainly adequate and is a great convenience -- it's one of the reasons I ended up with the RR in the first place. Once I decided to go wireless, however, I needed a solution to improve the quality I was getting from Airport Express, which is a great and virtually painless appliance that happens to have a very average DAC -- less impressive than the one in the RR.

There is no question that the DAC Magic does a better job than either of the two previously mentioned DACs. Highs are more precise, lows are lower, stereo imaging is a step up.

Plus, and I don't really know how to technically explain it, but the DAC Magic removes a lot of what I consider to be "the MP3 sound" -- the sort of hollowness experienced in lower-quality MP3s, like you're listening to music with a tin can to your ear. I burn everything to either 256kbps or Apple Lossless these days, but I still listen to the occasional lower-quality download and the DAC Magic makes previously painful tracks listenable.

Personally, I wouldn't hesitate to purchase the RR2150 with the intention of going USB from your Mac. I was quite pleased with it before I moved to the wireless setup.

Hope that helps.