Airport Express only has an optical out but no coaxial, and I think that limits it significantly. I use one with a Lite DAC AH and its fine for casual Spotify use, but I've recently found that if I use the same DAC with a modest cd transport linked by coaxial it is much better, in fact quite extraordinarily good for the price of the DAC (and would be for a much higher priced DAC). I believe the Squeezebox has coaxial out and I'm probably going to try one myself for that reason. An AE is a handy little thing, but I don't think it is capable of being a primary digital source, though I'd certainly welcome correction from anyone who has found a way of optimizing its capabilities.