What's the easiest way to sync music to my phone? I'm now on CM13 (Android 6) and rsyncing in will not work due to permission errors (and the sudo command doesn't exist) So I ask you, are there any programs to sync my music across? I don't want to use services that require me to upload it and then download it again due to bandwidth and speed issues.

I have also tried adb-sync but it just errors out (as is expected with adb!).
You could use Bittorrent Sync to copy the music folder on your computer to your phone. The whole thing will complete on your local network (as long as you don't leave it!). I recommend Bittorrent Sync assuming your local network's speed isn't an issue.