I added XM to my stock Monsoon headunit 2 years ago and love it.

I bought a XM reciever from Best Buy:
   Pioneer
   GEX-FM903XM
   Universal XM Satellite Digital Tuner System
   (may no longer be available)

I converted the CD-CHANGER port on the Monsson headunit
to RCA-INPUT with the GM9-AUX adapter from PIE.

I converted the Pioneer IP-BUS OUTPUT to RCA-OUTPUT
with the PIO/P-RCA adapter from PIE.

To connect the two, I just used a 12 foot RCA patch cable I bought at Best Buy.

I also installed an Install Edge IECALD Adjustable Line Driver "Pre-Amp" that I bought
at BestBuy's install garage to boost the audio signal to match the CD and FM volume output.

Cost Breakdown:

Pionner receiver $100
Terk slim XM antenna $50
Adapter Cables $110
12ft RCA Patch Cable $20
Pre-Amp/Line-Driver $20?

Total $300

I did it in stages to break up the cost. I installed the receiver using the built-in FM transmitter for a while, but eventually got fed-up with the static and noise that would creap-in over FM. Then I bought the adapter cables. The sound quality is much better because it is a direct connection.

There are other (cheaper) setups available now. A great place to buy XM stuff and Adapter Cables is http://www.myradiostore.com. You can find installation kits there now instead of piecing it together like I did.

Bellow are pictures of the items...



Pioneer XM Receiver Display





Pioneer XM Receiver
(before the adapter cables)



Current (hidden) location




Terk XM Antenna
(Hidden inside Formula Wing)





GM9-AUX





PIO/P-RCA





Install Edge IECALD Adjustable Line Driver "Pre-Amp"