OH just to clarify, the six moon review claims that the signal out of certain toslink cables (Wireworld superNova and Van Den Hun Optocoupler $100) are at least equal to much more expensive co-axial cables.
Since the AE only streams digital out of it's mini-optical (toslink), there is no USB audio out (only printers), this pretty much rules out all the USB and co-axial DACs.
The Pacecar you put between your DAC and your pre-amp/integrated amp is like $1000+ dollars. That's a lot of cash. And I really don't know about spending thousands+ dollars on an external DAC.
I'd rather use that money for a quality turntable if I really wanted a superior listening experience, because no matter what, dollar for dollar, analog is going to sound better than digital.
I use a Macbook, and sitting on my couch being able to stream audio wirelessly while I'm surfing the net is pretty wicked. There's no way I'm running a USB cord to my stereo.
Also for all you non-itunes users, there is the Airfoil program (google it) that allows you to stream programs other than iTunes through AE.
Hope this helps.