iPod, iMac, and JBL Creature II speakers

I have been using my iPod for over a year and will finally be getting an iMac later this week. I am looking for speakers that can be used for my iPod and the iMac together. It looks like the Creatures have only one audio input, but could you use a splitter to input both the iPod and iMac into the same port? I would love to be able to just use the iPod to play music with my Apple Dock but also use the same speakers for my new computer as well without having to disconnect the input each time.

Thanks for helping me figure this out.