My computer is a new 13" MacBook Pro. My router is an Actiontek PK5000. I use 3 Airport Expresses to connect 3 sets of powered speakers to my network. I use my iPad for interface with iTunes for my music collection and for internet radio. All speaker sets work fine independently. When I select more than one set at a time, the speakers sometimes work fine, but at others cut in and out, sometimes separately, sometimes in unison. Anyone have a clue what the problem might be?