I have a aftermarket stereo that is sat ready, but when i had it installed the guy at best buy said that the factory antenna wont work on my head unit...is there an adapter that i can use or what exactly to get my stereo to work....
no, best buy is incorrect, and its not so much ignorance as it is no experience with using OEM equipment on the aftermarket gear they sell.
any OEM SAT radio antenna can be used on any aftermarket SAT tuner, adapter cable type is based on the model and year of the vehicle being adapted.
also, most ALL Sat antenna are adapted to a separate aftermarket SAT Tuner which is inturn connected to the aftermarket headunit, and located in a different location than the headunit itself.
but it is a very easy adaption with the right antenna adapter and can be done by you, as it simply involves disconnecting the OEM XM or Sirius SAT antenna lead from the OEM SAT Tuner, and running an adapter from that OEM lead to your aftermarket SAT Tuner.
simply plug-and-play, nothing more-
be honest, Best Buy should have adapters on hand as you know SAT enabled vehicles are coming in for aftermarket gear installs, and why mount another external mag mount antenna when you have one already mounted on the vehicle?!