The XD600/1 is the compact class D model and they are probably 10% underrated. The JX series is the JL entry-level series and it is class D as well. I have no idea if they do rated. Obviously the JX 1000/1 should be louder based on claimed output. Neither are stable at 1 ohm so, keep that in mind when buying subs. If you need the additional power, go with the JX. If you want a very small footprint (and easy to hide), go with the XD. If you have a JL dealer in your area, why not listen to both yourself?