Are there any iTunes alternatives that can easily find and use multiple AirPlay devices in a multi-room system? Ideally, I'd like to find something that gives me more flexibility in formats, and is just a pure music player.
From what I read it sounds like you want to use Airplay with your devices outside of iTunes?
I know with Mountain Lion and newer you should be able to stream all your Mac's audio over Airplay simply hold the 'option' key when clicking the sound/volume menu, as long as your device is Airplay compatible it should appear in the list of available audio outputs (this should work with Airplay speakers, AppleTVs and Airport Express units.)
I'm not entirely sure of the ability to use multiple Airplay devices in synchronisation. I hope that's of some use.
Are there any iTunes alternatives that can easily find and use multiple AirPlay devices in a multi-room system? Ideally, I'd like to find something that gives me more flexibility in formats, and is just a pure music player.
It's not an alternative to iTunes (not a media player at all) but you might want to look at Airfoil as it would open up your options for a media player.