jaggerwild

Hey Jess,
guys at best buy (no offense if anybody here does) don't know all that much really. The 50x4 watts means that it has four outputs for speakers, total of 200 watts. Most units are four channel too so.......... Cheap ones may not be.
Preouts are for an Amp to amplify the sound to a bass box or replacement speakers too.
The car kit usually has all you'll need, some cars have special needs but not all. Let them know what car you have to make sure that you will not need other pieces for it. The secure thing I've not heard of.

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JAGGERWILD