My stang came with Factory sirius and Nav, and it works seemlesly, very good integration between them. My 2008 Expedition came with the factory radio and I had a Pioneer AVIC-900BT installed by a small shop, the integration is not smooth. It would be difficult for someone not trained and experienced with the unit to get in and change radio sources and select destinations, or make a change on the fly. The bluetooth aspect works pretty well IMO on the Pioneer. Of coarse after I bought the Pioneer and started to learn about all of it's idiosynchrities I discovered that the pricier Kenmore Units may have been a better solution for me, for the ease of use aspect. The Pioneer also lets you add Sirius as a add on module, but I have mixed reviews about it.
One last note about the aftermarket Units, and this is something that I never even thought about as an option or something that wouldn't automatically come on expensive new equipment. It is the current Artist and Song Title info that terrestrial radio plays does not show up on the Pioneer as standard option, and I was pretty irritated about that. I believe it is possible to have with a different module though.
08 GT Vert, Manual, PerfWhite, RedLeather, ClothTop, I-UP, ActiveAlarm, HID's, HeatedSeats, Scoop, Sirius, FoMoNav, 18"PolishedBullitt's, AmbientLights, GentexMirror(Electro/Comp/Temp/Homelink), JaegerFlaps, CPCHoodlifts, CDCWindDeflector, FRPPCAI/Tune, Shelby/Drake STB, JLTOilSep