The 600 will reach 6Hz lower than the 500. It will not go louder than the 500. If you want to feel infrasonics in movies, or listen to pipe organ, go 600. Otherwise, the 500 will reach down to 18Hz which will give you a nice vibe. You will not be able to hear that. Depending on how old you are, you may not even be able to hear 20Hz.
All Axiom EP (sealed) subs have the same sound: smooth, deep, tight, fast, transparent, undistorted bass that doesn't draw attention to itself but rather blends with the rest of the material no matter how much the volume is turned up.
These subs also have a "boost" mode which allows you to turn up the mid-bass if you so wish.
