hmmm this sounds a little like a problem I had...

I've got a linksys router (running DHCP) though instead of WinProxy.

What I wound up doing is decreasing the number of DHCP clients the router can serve (dropped it to like 16, in the range 192.168.1.10 to 192.168.1.25), then set the PC that is running the receiver manager to a static IP address OUTSIDE the range of DHCP addresses (192.168.1.50) and then telling it to serve music to receivers in the range of DHCP (go to "tools"->"IP Configuration"->"Enable Autoconfig")

But it could be some other part of my setup that forced this solution (I run wireless to one receiver)

~fiddy