Yes you do lose your oil life, etc...
I would honestly recommend just getting an external gps like tomtom, and keep your factory stereo.
As for the speakers, those are pretty trashy, but none the less a little better than factory ones. And those wont fit in the rear deck either, rear deck speakers are 6"x9"
2006 G6 GT
Mods so far: Black arrow overlays, Chrome recessed grilles, Blue LED license plate light, Blue LED reverse lights, Smoked tails, 20% Tint all around, Red led's for the interior, White led dome and map lights.
Sound System: 4 Infinity Kappa component speakers, 2 Amps (950w total) and 2 10" Kenwood KFC subwoofers, 7" touch screen Pioneer DVD
Performance: Mobile 1 oil, Mobile 1 oil filter