yeah, have you checked each pickup by itself?
wired right, they each should work fine, but together you'd probably only hear the "X" pickup.
(i discovered this when wiring a set of duncan blackout (active) guitar pickups to an EMG-equipped axe; the duncans conveniently use the same connectors in the same configuration into the same pots, so i only had to clip in the new pickups; as an experiment i left the EMGs in to see how they mixed, and the duncans completely swamped them.
the blackouts have a newer preamp than old-school EMGs; i suspect they were part of the impetus that got EMG to upgrade their preamps with the "X" series.)
here's a dumb question: is the connector clip in backwards on the JX?
Guitar Repair Gnome
Alpha Music, VA Beach