You have a couple of options for getting them to work with an aftermarket HU. I believe there is a direct plugin version for Alpine HUs. Others require that you use a universal kit that basically takes a IR signal and interfaces it to the steering wheel controls. You can then program each button to do whatever you like from the aftermarket HU remote control. Here is a link to some more info from Pac-audio.
I just hooked up a Pioneer headunit with the PAC SWI-PS. It works great. My suggestion would be to call Crutchfield and talk to them. They have excellant Tech support and the prices are pretty good considering that they also provide the wiring harnesses, dash kits etc. Make sure that you hook up a 12v switched power lead to the "antenna power" (pin 5 in the harness) or you will have poor radio reception (especially AM). Crutchfield & myself just figured out that there is an antenna booster that needs to be turn on this way.
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