Navigator 2003 - Adding Sat Radio

I am adding a Sirius Radio to my wifes Navigator. 2003. It has full Sat Nav, touch screen and all that.

How easy is it to add the modulator I've bought inbetween the ariel and radio and where can I pick up power that will go off when I take the key out.

I went the modulator route becuase there does not seem to be an aux in on this touch screen factory system.

Is this easy? What panels should I remove and how ? Are there any instructions anywhere ?

Thanks ever so much