Maybe I'm last to get the memo, and this is old news.
I missed my Audio Switcher program
[link] that I had on my G5 music server, so I finally downloaded the latest version for my iMac. It allows you to select outputs and inputs right from a menu bar pulldown instead of going into Audio Midi Setup.
But Surprise, in the Audio Switcher READ ME, it informed me that OS 10.6 (and later) had some of its functionality built in. Really? Yep....
Just hold down the OPTION key while clicking on the menu bar Volume icon and it changes to an Audio input and output selector, shown below.

*I have two DACs connected to my iMac: one Toslink in the office, the other USB for the main system, which I choose between.