It will hinder you GREATLY. Here's why. For one, the stock HU is only 25wx4 channels. 25w is pretty crappy, and especially for those speakers you'd like to get. Sure it will sound better than the stock speakers, but the db level of them will be less which means it'll require more volume to make them just as loud. Keep in mind you are already pushing the wattage limits of the stock HU which is why you hear distortion, or clipping. This is why you'd need or want an external 4-channel amp. Ok, you have a 100w amp built into your stock HU to provide the power to all 4 speakers. 25wx4 to be exact. Look at the space that amplifier is in. Now look at the space say a 40wx4 (or 160w total @ 4ohms) has the amp components in. Much bigger, right? It's all about capacitor size inside the amp also that makes a big differance. You can't fit much size of ones in the stock HU. So this is why an after market one is better, it'll have the pre-outs to accomidate an external amp, as well as have a beefier internal amp to start out with. My Alpine HU I have has a 50wx4 challen amp, opposed to the 25wx4 that my stock HU I replaced had.
Hope that makes some sense to you.
