iTunes Alternatives For Syncing Music?

Hi all,
Can anyone recommend some Mac-friendly alternatives to iTunes? I've been plagued with issues syncing music since getting my iPhone 6 back in the fall (music corrupts and appears as other, album artwork deletes, all music deletes except files purchased in iTunes, getting stuck onWaiting For Changes To Be Applied, etc). Yesterday Apple replaced the phone, yet the same issues are occurring. I know they're pretty common and from what I can gather going through the various forums, they're not out of the norm right now and will continue until Apple addresses and fixes the software bugs in iTunes and iOS 8.

Until then, I have a large music library (I'm trying to sync a little over 13,000 songs of it right now) that, for the sake of dramatics I *need* on my phone, and I'm searching for some insight on alternatives to sync the music. I tried doing it through Spotify Premium but their transfer process (via wi-fi) and the way it takes up space on my phone (which is greater than iTunes/ the Music app per song) don't seem to be the fix I need.

Can anyone make some suggestions? I'd be willing to pay for something, but if it's free I wouldn't complain.

UPDATE:
I've tried iMazing, but it only works occasionally. Sometimes a playlist syncs, most times it doesn't. Isn't exclusive to certain playlists or sizes of playlists. I'm attempting to get a refund from them.

I've also explored a few other options including TunesOver, AnyTrans, TunesGo, and Sharepod and none of them quite seem to suffice.

Spotify has a bit of potential, but from what I can gather it can only sync over wifi and it's a very slow and grueling process (I've tried on 2 different and separate networks so far).

I feel so powerless and lost without my music. Apple is just leaving us out to dry, and it's extremely frustrating. I bought this phone for the size to sync my music.