Using Airport Express/AirTunes.

Airport Express has, according to Stereophile review, decent low jitter optical out and less then perfect DAC (what can you expect for $99). It has two problems: Limitation of 16/44.1 and lack of clock between songs resulting in a loss of few seconds of next song when DAC is slow to sync(crossfading in Itunes being remedy for this). My Benchmark DAC1 doesn't do it and all my music is 16/44.1 but when higher resolution downloads will become more popular I might switch to Apple TV (that costs the same) or similar. AFAIK AE uses ALAC format for transmission - that is my storage format. Remember during installation to "join existing network" instead of creating separate network. Also figure out frequency of your microwave (manual) and switch to channel far away - unless, of course, you can use 802.11n that operates at 5MHz. Unfortunately I have old Mac Mini that does not support it.

Sfar, I agree 802.11n is the best option since I have dropouts with 802.11g (on occasions only). 802.11n is using 5GHz (5MHz in my previous post was a typo) - less polluted band far away from microwave ovens and cell phones.

Sfar, It might be dependent on the DAC used. All of them suppress jitter by means of PLL or asynchronous resampling - some more some less. According to Stereophile review test AE is bit perfect so jitter is the only possible difference. Benchmark DAC1, I use, supposed to be jitter immune but many people reported different results with different transports. Since results were not in par with the price (that has some correlation with jitter) and often very cheap players sounded the best - it makes me believe that there might be something else going on (ground loops etc). On my system I cannot tell the difference between AE and DVD player used as a transport - they sound identical.