Apple has their devices locked down preventing third-party software from syncing to iOS devices in the way you want. No amount of paying Apple is going to get them to open up their walled garden this way unfortunately and a US-based company like JRiver just can't find and add some sort of hack or workaround allowing them to somehow sync either, as Apple would just sue them into oblivion. The honest brutal bottom line is this... if you don't want these sort of issues don't invest in walled garden platforms like iPhones or you'll have to deal with the limitations of doing so, this being one of them.
In order to sync to iOS devices like an iPhone you'd have to use Apple apps like iTunes or Apple Music unfortunately.
