Satellite radio and Prius II

I got the basic prius II which is not equipped with satellite radio (or a nav system screen etc). This is my first prius so forgive me for any ignorance, but I need help/advice. What is the best/cheapest way to get satellite installed? I already have a sirius subscription (with a stiletto device). This came with a vehicle kit, which I could use in the prius.. But why would I need the vehicle kit if the prius has a satellite antenna already? Also, since I Dont have the ipod usb option in my prius, is it worth adding the ipod interface kit at the dealership? Or should I just use the aux jack and control the ipod on the actual ipod device (as opposed to controlling it with the steering wheel and factory radio). Additionally, I was told by the dealership that I cannot use the ipod interface kit if I have a sirius radio connected, and vice versa. Basically telling me i have to choose one or the other to have installed in the car. Please help? Advice or thoughts anyone? Much appreciated.