Yes all GM radios have the auxiliary audio input the problem is that the wiring and module is not in the vehicle,this port was there for the rear dvd system
and you can plug this into the 12 pin plug on the back of the radio
use this http://www.oemautosound.com/pc-296-83-piegm12-aux-chevrolet-2002-2007-auxiliary-input-adapter.aspx Good luck and just order the Trail Blazer module, since Envoy was not mentioned.