Grab a surplus receiver with a 7.1 channel analogue input. Split the signal and create a poor mans 3 zone amp (more if you can mono the signal). After you've split the signal then turn each zone on using a relay controlled by the PIR. Set the run time with something like this:

[Link: ebay.ca]

12V LED Digital Programmable Timer Relay Switch Latching Self-lock Module Board

Craig