I added the Ford Sirius Radio Kit to my Thunderbird (also a 2004 with
the "Sat" button). It is a seperate receiver and antenna. It is
operated through your regular radio controls. When you press the "Sat"
button, it is like changing from AM to FM or CD. The controls now
operate the satelite recevier. Go to
http://www.radiosandmore.com/prod_detail.asp?pn=4047452 and take a look
at the Sirus reciever that works with your head unit (it is a Visteon
product). The Visteon product description pdf can be downloaded from
http://tinyurl.com/byr3r (this is for Sirius Radio). Go to
http://tinyurl.com/ey9rz and look at the bottom of the page for
additional information on the Visteon unit (including the operators and
installation guides). Radiosandmore also sells XM solutions that will
work with your Ford head unit.

You could just go aftermarket and repalce everthing. I have done this
on one vehcile. And on a third I have an add on unit that goes through
an RF modulator. Of the three, I like the Ford radio with the add-on
kit the best.

This is a very spendy option (here in Canada, anyway). It's very intrusive
to install, also. The only benefit is that the satellite info and controls
are all in the radio with no extra visible additions.

I've installed two on new vehicles.

I had one installed yesterday, cost $99. works great, the satellite
controls are on the existing unit if it's "satellite ready".