Adding new stereo head unit with existing infinity amp
 

I'm new here so Hi to everyone.

I have a 98 Sebring JXI convertable. I want to install a new stereo head unit. With what I've read online I'm confused whether I can use the existing factory amp with the new head unit. I'veread some placesit needs to be bypassed. True or false? I've looked at the amp and it's wiring is not what I'm use to seeing. I'm not a pro at car audio so maybe I don't know nothing. Most amps I've seen are wired to the head unit with line level rca cables. This amp looks more like speaker level connections. If I can use this amp can I assume that places like crutchfield and best buy will have the wiring kits I should need for easy instulation? Anything special I need to do?
Other related questions.
Are there any High pass, low pass adjustments that can be made on amp and were would they be?
I already replace the rear speakers with a couple of 4 way 6x9's. I went online and found a page that told the wire color codes for pos and neg connections. The left rear wire colors did not match the what I readonline. Does anyone have wire schematics for the audio? Chilton book does not show them.
Thanks