They are different from what I understand. The one behind the seat is just a charger. I suggest that you look at a few after market additions to control or add music devices...
Clarion Remotes (need a Y cable, 30$) I bought the waterproof wireless remote.
( there are others like this )
GPS Bluetooth (requires Navionics iPhone app or other compatible map app)
(there are others, I like this one)
eBay or Amazon have better prices than the sites above...make sure you buy the right accessory compatible with your head unit, likely the CMD6 Clarion.