I used and prefer Schneid's method:
http://www.titantalk.com/forums/titan-interior-discussion/16070-photos-simple-xm-install.html?highlight=knee+plate
Look under the driver side dash carefully with a flashlight. I think you already have the NBUS cable (the RF system is pre-wired) which is connected to the back of the HU. That cable gets plugged into the XM receiver.
When I bought the OEM Nissan XM receiver, it came with some little angle mount brackets. If you want to do it the hard way, there is a special bracket to mount the XM receiver piggy back on the Rockford amp. I have done it that way also. It is somewhat of a PITA as the amp is way up on the firewall under the driver side dash.
The only other thing you might need is an antenna splitter depending on the connectors on the antenna cord and the XM receiver. I had to get a splitter, maybe they have updated the XM receiver by now?
I put the antenna on the roof and ran the cable through the third brake light and under the plastic trim strips. I used two popsicle sticks, one to lift the edge of the strips, and one to poke the antenna cable under the strip. To do it that way, you need a small deep metric socket to unbolt the third brake light, (7 or 8 mm, can't remember which).
http://www.titantalk.com/forums/titan-interior-discussion/16070-photos-simple-xm-install.html?highlight=knee+plate
Look under the driver side dash carefully with a flashlight. I think you already have the NBUS cable (the RF system is pre-wired) which is connected to the back of the HU. That cable gets plugged into the XM receiver.
When I bought the OEM Nissan XM receiver, it came with some little angle mount brackets. If you want to do it the hard way, there is a special bracket to mount the XM receiver piggy back on the Rockford amp. I have done it that way also. It is somewhat of a PITA as the amp is way up on the firewall under the driver side dash.
The only other thing you might need is an antenna splitter depending on the connectors on the antenna cord and the XM receiver. I had to get a splitter, maybe they have updated the XM receiver by now?
I put the antenna on the roof and ran the cable through the third brake light and under the plastic trim strips. I used two popsicle sticks, one to lift the edge of the strips, and one to poke the antenna cable under the strip. To do it that way, you need a small deep metric socket to unbolt the third brake light, (7 or 8 mm, can't remember which).
The one I'm looking at has one antenna connector. I'd post a link but the forum says I have to post 15 times first? *grumble* People can have avatars with nearly naked bouncing boobs, but no url.. (I like that avatar, just stating 
