Suddenly having issues streaming iTunes 12 (OS 10.9.5 / 2010 iMac) to an Airport Express

The Airport Express is one of the older ones (no power brick). I had issues 3 months ago ; Apple couldn't help me (before I had to go) so I left it at that. Thought to get the other Airport Express out of the garage (same model), plugged it in and it worked fine until...

Until I flipped open my laptop which is running Yosemite(!) Is this a coincidence? It looks like as soon as it tried to connect to the network it killed my Airplay. I've rebooted the iMac, unplugged and replugged in the Airport Express, etc. The Airport Express is joining an existing network. I'll be unplugging the Airport Extreme momentarily. Is this just a coincidence? Back when it initially happened, I though it might have something to do with Little Snitch, since I at the time recently performed an upgrade.

Any help is appreciated!