Check to see which DACs work with the Apple Airport Express. Some drop out and some do not. I think it is because of the lack of a clock in the airport express. I read this in the stereophile review. Try one that does not. Also check with Olive. They may know what works best.
BTW, how doe you like the Olive. Can you use it without a DAC. That might make the most sense if it sounds decent.
BTW, how doe you like the Olive. Can you use it without a DAC. That might make the most sense if it sounds decent.