Actually looking over the last couple threads here. Let me say that the package you buy the connector in usually has the wiring right on it. As does your new HU. Shouldn't need to fight it with a battery. (always a good fall back though) On the amp/gain, some of our cars are wired so you can not get any sound through the system w/o hooking up to the amp/gain or circumventing the entire amp/gain setup with brand new wiring throughout the entire car. I've hooked it up and it sounds good.
On the next one of stock is never good. I have an aftermarket HU and the stock speakers sound exceptionally good considering their age and technology at the time.
Every system can always sound better... or be enhanced to sound better. I'm fairly simple with it. I want it to sound good to me. My new HU and stock speakers do that for me. To change my radio out it took me about 15 minutes from one car to another. A simple unplug and replug.
00 Regal GS: All kinds of cool stuff.