i just got a couple for the front doors of my 94 grand prix. The guy at the store told me they are made on the same assembly line as Infinity. They sound pretty good. not as much bass as pioneer, but more clean and sharp.
I would grab the Infinity's over the JBL's. YOu can get Kappas real cheap on the internet, like eBay. Crappy amps will produce crappy sound, especially if they are underpowering a sub. You can get the same sound out of a 4 channel as you can out of a 2 channel.