iOS devices are not supported by MC. They are encrypted and locked to iTunes by Apple, and they've actually legally pursued commercial companies that have broken the encryption in the past (not to mention that it is a never-ending cat-and-mouse game where the cat is a 600 ton Gorilla with billions of dollars with which to smash you).
MC supported the very first iPhone and the early iPod Touch firmware (v1x), but Apple continually changed the firmware to intentionally block this kind of use. They want you to use iTunes to sync music to your phone. Period.
This, of course, only applies if you use the built-in music player, however. JRiver does have a very nice app in the App Store called JRemote that you can use to both remote-control your copy of MC over the network, and stream from your copy of MC to your device. In the future, they may add local caching so that it can play even when the device (or server) is offline, though it does not have this functionality at this time.
Still, though, if you typically have a network connection where you use your device, JRemote works great. I very rarely have to pull out Music.app and don't typically have much synced to my phone anymore.