My second thought was "put away the multimeter and turn up the volume knob."
If the speakers you bought had a lower sensitivity (dB @ 1W @ 1meter is usually how it's listed) than the older ones,
Then it would make sense that they would be a little quieter than the old ones.
This is the kind of "sensitivity" that scottmandue is talking about. How loud a noise a certain speaker makes given the same amount of power put into it.
"Sensitivity" on your JL setup is not the same thing, but if you set it up like in the instructions it'll be great. Set up the trim on the amp and then turn things DOWN to get the balance you want. If you turn UP the trim on the amp you might clip the input stage of the amp at higher volumes and it won't sound as good as it could.
have fun!