I bought a plug and play unit from Integrated Solutions on ebay. It works great, is easy to install, adds another AUX input, and allows use of the steering wheel controls and touchscreen. It is a much easier install than the factory XM module.
I also installed the integration solutions module on my 08 plat. Works great, easy install. Followed Big Vics thread on install. Easy. Only difficult part I had was fishing the antenna through the firewall and into the cabin. But that's just me. I mounted the xm mini tuner in the center storage bin so I can get at it. You can use it w/ a home docking station and an xm ready reciever or radio in the house.
the best way to fish the antenna cable thru the firewall is to use the rubber grommet on the passenger side - just cut the tip off with scissors. if you compare it with the one on the driver's side you'll see (at least on my DC) that they both have places to run a cable and the one on the driver's side already has one running thru it. Also, you can run the antenna cable down the rubber strip on the passenger side and then under the rubber strip on that side of the windshield. I used 2 credit cards held together with one slightly lower than the other so that the lower one opened the edge of the weatherstrip and the other pushed the cable under it. It worked very smoothly and I was able to run the cable in about 5 minutes total. I did have to lube the cable end to get it thru the grommet hole with a little silicone spray since it's bigger than the hole - this was a sirius antenna, the XM antenna might go thru more easily.
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DC Limited 4X4, TRD Supercharger, TRD sway bar, TRD Dual Exhaust, HID Xenon headlights, ARE tonneu cover, Sirius, Escort 8500
Vegas - How's your reception in that location? Sounds like a cool place to put it and you won't have to mess w/ the firewall. I suppose it would be easy enough to test it in that location and see how the reception is.
Antenna will probably work fine under the plastic speaker grill. The disadvantage is that these antennas like to be placed on metal ground planes (car roofs) to get the strongest signal and perform at their best.
I actually picked up a small 2" x 2" magnetic plate (iron metal) from the local ace hardware and drilled a hole in the corner of the plate and used the speaker screw allready mounted with and the antenna sticks right to it. I have great reception no issues. I noticed that the volume is lower than than fm and ipod music though.
I tried that location too but living up north the reception wasn't very good, thus the switch to the roof with far better results. I would think as a general rule the further south you live the better your reception is likely to be... and the fewer big trees, mountains, etc around the better.
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DC Limited 4X4, TRD Supercharger, TRD sway bar, TRD Dual Exhaust, HID Xenon headlights, ARE tonneu cover, Sirius, Escort 8500