You can buy the tuners mentioned, or, you can wait a month and the adapters for the xm commander will be out.. Basically xm cut out the middle man (pioneer, alpine, sony) and put out their own box, which btw has a foot print just a little smaller than a cd case..
Basically, buy the xm commander, buy the pioneer adapter, plug it in and thats it.. That way you don't have to sacrifice a lot of space.. Speaking of not sacrificing space, terk came out with a new antenna that is awesome as well.. (Comes w/ the xm commander) Its about the size of a silver dollar and half an inch tall..
Justin