I have OEM SiriusXM facotry head unit, but I want to get aftermarker

Do I need to purchase the " add a xm kit" like this one or can I hook up an aftermarket unit to the existing SiriusXM sharkfin antenna that is all ready on my roof?

If I have to get the additional kit, is there a way to keep the sharkfin? Just trying to avoid having two xm antennas on the roof.

thanks....


and actually recently came to the conclusion to replace the factory h/u even though its fine. Messing with a signal processor and line converters seemed to not work for others.

 

http://www.tss-radio.com/products/lexus-gs-shark-fin-antenna-adapter

 

thanks rellik, have you or anyone else used one? Seems to be the perfect fit for my needs.

 

I used it to connect an Alpine radio to the stock XM antenna plug and play