mixplayd is a multi-channel mp3/ogg player daemon controlled over a tcp port. It has all functions like play/pause/stop/seeking plus special mixer functions. The number of channels and sound devices (including named pipe support) can be changed at runtime.
Kaffeine is full featured Media Player for KDE. It supports all kinds of local and network media and digital video broadcasting (DVB). At the moment Kaffeine can use xine-lib or GStreamer as backend.
...This lets you have multiple UIs, multiple player types, multiple queueing systems. The ultimate conclusion would be a build your own jukebox kit. Includes a back end that Gronk! can