Does your HL already have a sharkfin or whatever on the back end of the roof? If so, then your system is already prewired (likely XM) for satellite and you likely just need a Fit Kit.
The Fit Kit will integrate with your head unit and allow you to control channel surfing etc from it.
Here's the XM fit kit:
http://www.trdparts4u.com/scripts/pr...product=326684
However if you choose Sirius (I would), you can order the Sirius Fit Kit, but if your system is prewired for XM, I believe you need an XM to Sirius converter. Not exactly sure about much more than that. You may also need a sharkfin antenna adapter.
Converter is here:
http://www.tss-radio.com/products/to...erface-toy-sc1
Adapter is here:
http://www.tss-radio.com/products/le...ntenna-adapter
Don't take my word as Gospel, this is just from what I remember when I had this same issue.