What are you looking for in terms of sound? You want it to be louder, cleaner, more bass?
The sound quality will be better, Bose does officially make great speakers. NASA uses them, even. However, I learned the phrase "All highs, no lows, gotta be Bose!" while I sold home audio products for a while, and they've earned it for a reason. If it's a bit more boom you're looking for, just add a sub. How to do it, however, isn't my specialty. Also, remember that for the audio upgrade price on a car, most of the time you can buy some great speakers and an amplifier and put a good system together yourself.