Hooking up multiple ipod hifi's... is it possible

I cant see a reason why you cant do it, it is matter whether you are going to please with its sound performance.

the simple way - you can buy a minijack splitter, plug it with the headphone jack of your iPod, so you can you connect it with 2 iPod HiFi.

For better performance, you can connect your iPod via dock system into a pre-amp with multiple outputs -> and connect with multiple iPod HiFi

or take the headphone splitter cut the cables, and join both left cables(white and both right cables(Red) to each other, this gives full stereo sound form two ipod hifis one for proper left and one for proper right audio, buy an ipod dock put it between the speakers plug lead from dock to splitter then from splitter to left and right speakers independently, (or you could just use the computer you have as the source).

this works very well, the ipod hifi really is an underrated apple device its difficult to get your head round but when you do, it really is time to chuck out your old stereo.