Explained as a new way for teenagers to share and mix music with friends, Belkin's RockStar ($20) is a star-shaped audio hub that lets people connect their iPods (or other MP3 players) and headphones. Multiple playback devices can be connected to the hub, sharing the audio from each source simultaneously with multiple headphone ports, and letting users hear either a single song, or multiple songs mixed together. One of the ports is input-only, with…
