The Squeezebox is available in wireless and wired versions, and it has both analog stereo output and a digital output (the current version of the Squeezebox has apparently got some really nice DAC's if you don't want to part with a digital input on the 990). It uses a program on your computer to organize songs into playlists that can then be accessed, and the latest versions offer pretty decent support for different file formats as well as streaming audio stations. The Roku Soundbridge is similar (wired and wireless options), but I think it just grabs stuff off of network drives. The Photobridge can even handle HD resolution video files if it has an ethernet connection (needs more reliable bandwidth than the typical wireless network can provide).