The PAC unit uses the Sat Radio input on the '05+ Rockford Fosgate units, the '00-'04 RF units did not have Sat Radio as an option from the factory. This is why there is no where to plug the PAC unit into...not having looked @ the back side of a first gen RF unit, I can't say what other options you might have for an aux input, but all I've heard about so far is the in-line FM modulator mentioned already in this thread.