Speakers are a pasive devise. Curent flows throught them. Different speakers will sound different. But if you take and install an amp but not change the stock deck, you'll be amplifieing any inperfections from the stock deck! I have done this in the past, I didn't want to change the look of the factory dash. But after speakers, amps, and subs, I still wasn't happy. I then bit the bullet and installed a new deck. WOW, the system came alive!
A new deck of good quality puts out cleaner sound, that can be amplified to sound better and inturn save your speakers.
A little something to think about when your listening to some systems. when you turn it up, and it hurts your ears, thats bad! if it urts your ears, the speaker is hurting! Now a good system is when its turned up, and you can't hear your self talk, or even yell, and it doesn't hurt your ears! Thats quality! And when it comes to load, clean music, you HAVE to start with a top quality deck.