Installing new stereo

Ok I'm sorry if this has been asked 1 million times, I am feeling over whelmed right now.

I have a 2004 avy with on star and steering wheel controls, no Bose. I have a  new dual brand double dinn touch screen sitting on my work bench, and I can't find the right adapter.

Can someone please help me find the right adapter that I need to hook to the factory harness. 

crutchfield.com...

Pacific Accessory Corp.
http://www.pac-audio.com/productSearch.aspx?Make=Chevrolet&MakeId=4&Model=Avalanche&ModelId=1367&Year=2004&YearId=15

You can call PAC @ 866-931-8021 and they can walk you through exactly what adapters/harnesses you need.