AirPlay Became Erratic, and Now Barely Functions

I have several Apple TVs, all using PoE to avoid hogging WiFi bandwidth, which sometimes drop out when streaming music from my iTunes library.

But the real problem is my pair of AirPlay speakers. They used top work flawlessly, but now it's hit and miss as to whether AirPlay will even find them -- and even when there is a connection, it rarely lasts for more than a song or two.

I've check signal strength and signal-to-noise ratio, and everything looks great. My first thought was that my speaker was dying, but it seems unlikely that TWO AirPlay speakers would be dying at the same time and in the same way. And then there's the weirdness where the problem crops up (although not as badly) with the PoE-connected Apple TVs.

Anyone have a similar problem with your AirPort Extreme or Express? Did you find a fix?

Thanks!