I purchased a new aftermarket Kenwood head unit for my 2004 WRX. After it was installed, the am/fm signal went to crap. After some troubleshooting, the installer tech said that he thought maybe the factory Subaru head unit had some special power rating (which was @ 75ohms on the factory head unit) that made the antenna work better. He said that "no" aftermarket head unit would get the clean am/fm signal that the factory head unit was able to give. Is this true? So there is no way to have a good sounding radio signal with an aftermarked head unit and the stock antenna?