I've been mulling over this problem for a while now and I've got a workaround of sorts.
I bought a copy of Plogue's Bidule (
http://www.plogue.com/) product that allows you to host AU's and VST's.
Because I bought it I also had access to an AU version of Bidule. I was able to load the AU version on to an audio track in Live and send audio from that track to Bidule.
Inside Bidule I then added a AUNetSend AU.
On the other MAC I ran another copy of Bidule and hosted an AINetReceive AU which I connected to the AUNetSend on the source MAC.
I then processed the incomming audio and then used a AUNetSend AU to send the audio back to an AUNetReceive hosted in Bidule on the source MAC. Then I routed the audio from the AUNetReceive back in to the Live audio track.
Hope that helps.