It's a police bike so i am not sure if the controls are even in the housings...
I also have a '14 Police Glide and the volume up/down and next/previous controls on the left grip are there on mine, but the controls on the right grip are not.
I'm about to tackle this same thing although, i'm trying to do it with a bluetooth module that connects directly to the amp - no head unit. I will use the volume on my iphone to control that as well as next/previous and play music from spotify/iheartradio and music on the phone.
...that's the plan at least. Nice build! You answered some questions I had under that fairing.