I have daapd and a simple multicast dns responder basically working on the empeg.

I hadn't heard of DAAP before. That's well cool. It's a pity all the toolkits seem to be GPL (or Java); if there were a nice BSD-licensed library, and if I had anything to do with it, that stuff would be going in the stock Empeg and Karma firmware.

Presumably Apple decided that UPnP MediaServer was too much like hard work?

Edit: and to answer your question, get an Emptool distribution and look for lib/net/ipaddress.cpp's GetAddressForInterface(), passing "eth0". Or look up SIOCGIFADDR in your nearest W Richard Stevens book.

Peter