IMHO the best way to solve this problem is to integrate offline playback capabilities into JRemote. Then syncing entirely becomes:
* Unnecessary for most users
* Entirely within JRiver's control
Both of which are wins. No matter how good the integration with iTunes becomes (and the iTunes API is fairly stable, and has been for a long time), there's no guarantee that Apple won't up-and-discontinue iTunes entirely in a year or two.
In fact, I wouldn't be surprised to see that kind of thing happen at all, and for them to move to a "SyncToy" kind of solution, morphing iTunes itself into a Beats Audio service player.