The misunderstanding stems from the fact that that's not a tuner. It's a modulator or transmitter. A tuner receives FM transmissions. It's also commonly referred to as a radio. What you have sends them.

Since you already have a tuner (which I can tell by the fact that you're using it to receive the signals sent by the Jensen modulator), you have no need for the empeg tuner unless and until you decide to scrap the rest of your car stereo.