I'm thinking it's about time to put some new speakers/stereo and maybe a sub in my car. School me on good brands/and stuff. Unfortunately my car's speaker holes can only fit 6.5". Also, if I get a mono amp + sub do I need anything else? like a crossover or extra power/capacitors etc? I've been thinking of getting some Focals but I kinda wan to keep the cost low - as my car sucks.