[My Wife\'s Hummer]

i don't know about the xm/sirius together, but that would be cool. as far as the tuner, the factory one is up above the glove box, but you can only see it with the radio out and looking back into the dash over top of the glove box. box is fairly small. the dealer might have installed the pioneer tuner back in the dash behind/next to the head unit. that is where i am planning on setting mine. hope this helps.