Well, it seems that the stock amp on my 2000 ssei has blown. I have looked around several places to see what my best replacement options are and I came up with...

1) Amp #1 will be for the speakers inside

2) Amp #2 will be for a 10'' sub

3) Add a crossover

Now, I have an aftermarket radio as well as aftermarket speakers/tweeters. I don't want anything bigger then one 10" because I am not really into the heavy bass anymore. Do I need to get this kind of setup or is there a way to just replace the stock amp with an aftermarket one?

raptor will chime in he is the audio guru round here.
i would have to think if you are going aftermarket on a amp you would have to run new wireing and just bypass the factory stuff also if your not into bass and only running a 10in sub you could always go with a 5 channel

How many pre-outs does your HU have on it? It will require a minimum of two to be able to run two amps. It'* recommended to have three though so you can keep your "fade" capability.

I know the basics on setting up an aftermarket stereo, the thing is am I going in the right direction or do I need a different setup.....

I have the setup you have. One amp for my internal speakers and one for my sub. I know 5 channels are an option but I liked the idea of having a sub on separate power. Also, what was said earlier is right, you'll have to bypass the stock amp to make it all work.

yep you'll have to bypass the amp to make the cars stock wiring work, but when i did mine i figured i had to tear the car all apart to run the other wires and the stock ones are kinda small so i ran new speaker wire to all the speakers right from the amp. my hu has three sets of preouts so i didnt fool with the stock amp wiring just bypassed it all together. they do have premade bypass harnesses for some cars if you want to go that way.

i went with two amps too like mouse said, and its hard to find exactly what you want unless you want to really pay for it. and say you want to change to a different sub or whatever your locked in because you dont want to have to pay all that money again

When I was running two amps I just ran power/ground/switched to my radio, and didn't bother hooking up the speaker wire, just ran the RCA'*. No need for bypass harnesses that way.

I think two amps would look killer in the right setup, but for those that actually USE their trunk a 5-channel would more than suffice.

two amps dont take up that much room
https://www.gmforum.com/audio-aftermarket-electronics-101/working-my-setup-2-0-a-297777/

But they may take up more room than he wants to lose.

I don't think 2 12'* and 2 amps take up that much room but others would beg to differ.

How do you know how much he wants to lose?