From the Gadget Junkie website.
I started out with a Y splitter and 2 sets of amplified PC sepeakers but I needed a way to selectively turn the speakers on and off.
While browsing the HomeSeer forums I came across a link to a site describing how to build a CCTV camera switcher. This circuit uses a PC parallel port to operate switching transistors. I figured with a bit of tweaking I could use this principal to switch the output from a sound card to several pairs of amplified speakers”…
Read the rest here Gadget Junkie