streaming baby monitor audio over home network

I'd like to determine, for a variety of reasons, a way to broadcast audio out from a baby monitor over our home audio network (via AirPort). Mainly, I would like to be able to 'tune in' to the baby monitor channel using my iphone 4's Remote app. while working out in the garage (out of baby monitor's range... also hard to hear normal baby monitor with exercise equipment). We have an iMac (OS X 10.6.8) and my MacBook (OS X 10.5.8) on the network, as well as my iPhone 4 (vs. 5.0.1).

So... is there a way to make available (to my iPhone) an audio-in channel via ITunes on either the iMac or MacBook using the home network?

Thanks in advance for any help!