no superchargers, or turbos for a 4.8, only the 4.6 (due to valvetronic)
-Dinan is your best bet, but you'll only get about 20Hp for 6k

You can get either Dice (available through one of the site sponsors) or the BMW aux input (I have this and it works well b/c it's non-proprietary and I sometimes plug my laptop in)

You can probably go as wide as 335 on the back (I don't think there are tires available though, the best bet is to look at the tire specs and look where it has rim requirements at the min/max)

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2006 BMW X5 4.8is Lemans Blue/Beige/Dark Maple
-Nav, Comfort Seats, Heated Steering Wheel,
Rear Airbags, AUX Input
2009 BMW M3 Space Grey/Black/Carbon
-all options