07 and 08 XM tuner questions

I've done some searching around and have not found a clear answer as to where the XM Tuner is located on the 2007 and 2008 tahoe/yukon/avalanche models? I have a 2008 Avalanche and am considering replacing the factory head unit and would like to go to Sirius. I'm hoping to re-use the factory XM/Onstar antenna for this but am not sure where the unit is located so I can plug into the antenna lead? Also, does anyone know if the 07-08 year trucks have a single or dual input antenna? I did find the two adapter cables below:
 
http://www.tss-radio.com/sirius-single-input-antenna-adapter-p-3883.html
and
http://www.tss-radio.com/sirius-dual-input-antenna-adapter-p-3910.html
 
but wasn't sure which is used. Any info anyone can provide would be great. Thanks in advance!
 
Travis

not to promote the Coastaletech.com but they show a video of how to get to your Xm tuner factory location on the install video for the IPOD pick. 

http://www.coastaletech.com/iPOD%20iPHONE%20INSTALL.htm

Its behind the glvoe box and they show you how to get to it.  looks very simple..

FYI i couldnt use firefox to view the video, but it came up with IE

Awesome video, thanks for that! I'll go drop the box and see which antenna plug I need as well. Thanks!

you need the first one you posted.
If you have an 07 with the classic body style, it is behind the glove box. if you have an 07\08 with the new body style, pull off the plastic kick guard directly above passengers feet and the reciever is clipped in directly above

Excellent, Thanks for the info. It is in fact an 08 so I'll look under that panel. Glad to see a solid answer on which conversion cable it is. I have yet to get down there and look for it but I'll look under that panel and check it out. Thanks again.