Airplay on 2.4 and a 5 GHz networks on my Airport Extreme

I have 2.4 and a 5 GHz networks on my Airport Extreme, "Espresso" and "Espresso 5GHz." I would like to keep the library computer on the 5 GHz network but my Airplay devices on the 2.4 network. Strangely, this seems to work fine except with one stand-alone Airplay device; an Audyssy Audio Dock speaker. The speaker will usually connect but often 'fails;' that is to say, it will drop off the network.

Should I consider this an unsupported configuration and, as such, expect weird behavior?