I have lots of experience with the Jordan JX92S driver. It is a very nice driver with excellent smoothness and good extension into both bass and treble areas. You say low efficiency but it does have a rated sensitivity of 88 dB SPL 1 w/m. The free air resonance is 45 Hz which is exceptional. The Xmax (one direction) is 4.5 mm while the rated power handling is 50 watts rms or 100 watts music power. The JX92S can be designed into vented, sealed and transmission line enclosures with good success in all boxes. I've used the JX92S in a vented (or sealed) 0.25 cubic foot box for my mini-monitors. This design has a measured F3 point of 55 Hz which is excellent for such a small driver. In a 48" JX92S MLTL design the F3 bass extends below 40 Hz.
For example, compared to similar size Fostex drivers (I'll use the Fostex FE108E, FE127E and the JX92S in order) in the comparison below.
Bass extension (0.28 mm or 0.67 mm vs. 4.5 mm)
Power power handling (8 w, 15 w, 50 w)
Sensitivity (90 dB, 91 dB, 88 dB SPL 1w/1m)
Smoother frequency response (just look at the manufacturer's curves for an idea)
More adaptibility to various boxes
What is not to like about a driver that can cover a wide range--including bass and treble extension on its own--with excellent response and other factors? The Jordan JX92S kicks the backside of other full range drivers of comparable size.
Jim