XMBC parece um bom jogo para o que você quer. Ele roda no Windows, Mac e Linux, integra-se ao MythTV, tem muitos plugins, etc.
Do site do XMBC:
Currently XBMC can be used to play almost all popular audio and video formats around. It was designed for network playback, so you can stream your multimedia from anywhere in the house or directly from the internet using practically any protocol available. Use your media as-is: XBMC can play CDs and DVDs directly from the disk or image file, almost all popular archive formats from your hard drive, and even files inside ZIP and RAR archives. It will even scan all of your media and automatically create a personalized library complete with box covers, descriptions, and fanart. There are playlist and slideshow functions, a weather forecast feature and many audio visualizations. Once installed, your computer will become a fully functional multimedia jukebox.
Eu uso o XMBC no meu media center pc e funciona muito bem. Ele pode transmitir dados da internet ou de outros PCs, NASs ou praticamente qualquer coisa.