Airport Express (error -3256) trying to stream to multiple speakers

I have an iMac and have set up a network on airport extreme. Set up airport express to stream airtunes only and had no problem yesterday going to both computer and the speakers connected to airport express. Today, connected my windows laptops to the network with no problem using LinkSys wireless USB, but when I tried to stream music to computer and airport express both I got the error it seems many others have -- unknown error (-3256) and it will only now stream to one of the 2 locations (either computer or airport express, but not both at once) at a time. However, from iTunes from my windows laptop PC (I have version 7.0.2 on my PC, and just purchased my 1st iMac) I COULD stream to BOTH !! Now even when I disconnect the laptop PC's from my wireless network I get the same error. Some setting somewhere must have changed. I spent an hour on with Apple support and we looked at firewall, reinstalled iTunes, hard reset the Airport express and rejoined the wireless network, none of it worked. Since the PC laptop can stream to both, it must be the op system or some setting on my Mac.....shouldn't be the router.....should it? I am supposed to talk to Apple tomorrow and get the problem escalated when the hold times come down a bit, so if I can I will answer my question on this board, because I have seen similar issues that aren't solved yet (unless it was the firewall issue which didn't work for me).

Anyone who can help, please do. Or even suggest a course of action (maybe it is something with router? but then why did my PC laptop stream to both, or iTunes or Leopard?)......I have tried many of the obvious fixes on the phone with support. Thanks all.