New Member Needs Help with Stereo Subwoofer Issue

[Comanche]

Hello All,
My Name is Comanche and I have a 2001 BMW X-5 4.4 Sport. My BMW has a Business Radio, Business CD, 6 disk changer, HIFI Amplifier and HIFI Loudspeaker system. I contacted my local parts representative at my BMW dealer and asked if it would be possible to upgrade the speakers and install the factory subwoofer. He pulled up my X-5 on the computer and told me that I had the correct amp and the wiring harness , all I would need to do is get the speakers & sub and install them and plug and play. After finding the factory sub and purchasing it, I began to try to install by trying to find the wiring harness that plugged into my subwoofer. After searching the wires I could not find the amp wiring harness. I called my BMW Parts rep and he said that he made a mistake, I could not use the sub unless I buy a DSP Amp and a new wiring harness. Does anyone know If or how I can install a Factory Sub with my current setup? Please advise.

Thanks for your help. Comanche