how much are you willing to spend?
I wouldn't suggest cheaping out on a car like that! I'd go JL XR components. Slash series amps and depending on how much bass you like you can make a decision on the sub(s). JL subs sound amazing but are alot more for sound quality. I have 3 JL 10" subs and am extremely happy. As for a deck there is alot out there to choose from depending on how much you want to show off haha. I personally like alpine and kenwood exelon
haven't really thought about price, but I'll be ok with putting 2K into a good system if needed, with installation from someone that knows bmw's very well.
Hopefully someone here can recommend a place in GTA I can get it done at.... Othwerwise, I'll get in touch with my dealership to see if there is anyone that they recommend.