I have several years of experience working with Milestone products, and their stretch cards are often problematic with audio. So the way we get around it is to install IP POE speakers onto the network. (just add to cat5 cabling and onto a POE port in the switch).
Get a MIP plug in from Netgenium Systems that then enables you to use your push to talk command from any Smart Client and uses your Louroe Microphone.
You can talk to individual speakers - or even create groups of speakers its great.
The good thing is that you do not then need the amps so can deploy them elsewhere.
Go to this link for details.
http://www.netgenium.co.uk/Documentation/Collaboration/CoMilestone.pdf
if you email sales@netgenium.co.uk and ask for Glenn Fletcher he will let you know costs etc.
good luck.