Let's start with the JD series. The first thing you'll notice is that these amps are the lowest cost option of the three series. With the JD amps, you can get 1000 watts of power for under $400, whereas that same power will run you $150 - $300 more with the RD series and XD series. The best way to think of the JD series is to think of it as the base model amplifier. It's not going to have all the same features of the RD series and the XD series, but it will still get the job done.