Audio over Airport Express network which previously worked perfectly now cutting out, no changes to configuration made

I have my ISP provided device running in router mode only (WiFi switched off) with one Airport Express connected to it by cable acting as the wireless hub, I have two other Airport Expresses on the network, both running in client mode, one provides ethernet to my TV, the other streams audio to our kitchen from our devices which include: one PC, one Mac, a Wii, two iPhones, an iPad, and a printer.

In the last couple of months, audio to the AXP in the kitchen has been cutting out, but only when streamed from iTunes on my MacBook Pro, in the last week or so, it has played for a couple of minutes, then stopped completely. Then the Airplay icon on iTunes on my Mac turns orange.

My wife and I both stream audio to the AXPs from these various devices. Is there a cache directory or file somewhere that needs to be deleted occasionally on the system? It seem that the AXPs are getting confused by the numerous devices connecting and disconnecting to AirPlay.