MacOS – App-specific sound output devices

Unfortunately, there aren't any products other than the Airport Express that are compatible with iTunes music streaming (unless something new has come out recently). However, it's usually very easy to find a used model online for much less; I was able to pick up two of them on Craigslist for about $30 apiece. They may not be the latest model, but if all you're interested in is streaming music, then any model will work just fine.

I saw the chatter over on the official Apple forums last week and there has been some success on Retina MBP owners with the workaround here (and listed below)

Go to System Preferences -> Energy Saver -> Uncheck 'Automatic Graphics Switching'

This will of course switch 100% to the Nvidia chipset which will be a larger battery drain.

The issue, according to those users, is that the integrated graphics on the Retina MBP is the root cause and more than likely to be as a result of immature drivers from Intel since they also report that there is no issue under Bootcamp.