Yes, unfortunately when I try via the USB, the Samsung music folder is populated with hundreds of individual artist folders. I currently have over 1500 tracks on my phone and trying to add another 700. I would have to cut and past each artist tracks from my computer into their corresponding files on the phone. Probably an 8 hour job
As for the phone, mobilego worked with my previous phones (same carrier). Not sure why its not working with the S6 edge. I wonder if it has something to do with not having a SD card?
Yes, it is odd that they took away the ability to use a SD card with that one. However that shouldn't effect an apps ability to work. That said, it is completely possible there are changes to the OS added by Samsung that prevent it from working.
So it is not moving music to the phone that is the problem, but having it organized the way you want? Getting it to work in a specific app? Or both?