A very simple way is the use an Air Port (AE) express and itunes as Sfar recommends but you can connect it directly to one of the inputs on your pre-amp and use the DAC in the AE. The DAC of course isn't the best on the AE but does a pretty decent job for what it is. You can then evaluate if you want to go further expense wise. I currently stream Radio Swiss Classic using an AE to my stereo system and it works great.
Chuck
Chuck