you have to buy a device that will interface between car controls and the aftermarket deck.

There are several companies that make them, though the 'best' option IMO is Modifry's DCI because his doesn't require anything separate for the Mute button to work as normal. In my previous S2k I had a PAC SWI something and it worked fine for the main controls but I had to manually solder in a I think SPDT relay on the mute wire because most aftermarket decks expect +12v for mute but the S2000's mute button connects that pin to ground when pressed. Also annoying was that pressing Mute would mute the deck, but if you adjusted the volume after Mute was pressed, the button green LED would not turn off.

I believe Modifry's DCI retains stock Mute functionality.

 

For my Sony DSX-GS80, I bought these components from Modifry. You need the DCI + adapter harness. I recommend the PNP one and also the SCV kit.

Install was a breeze and it all works perfectly. 5/5 would buy again!

 

I have the Modifry PNP &SVC kit. I just swapped out my 10 yr old Alpine
for a new Alpine model that has Bluetooth and hands free calling. Everything
works perfect.