Airport Express constantly can not stream music from any device
I've seen that on a couple of them, and the problem seems to be tied to IPv6 support. Mine would drop connections randomly, sometimes requiring a reboot of the AirPort Express before it would return to the network.

Turning off IPv6 entirely in the Network Control panel of our Macs seems to have fixed it. I can stream music to it for hours now without problems, so give that a try.