I'm using it with your typical $150 10-inch subwoofer driver: a JL Audio 2.25-inch voice coil, Kapton former, 15mm one-way linear excursion, etc. It's a dual 4 ohm voice coil driver, wired in series driven by a bridged mono 160 watt Audio Research amplifier.
It's in a 1.4 cubic foot sealed enclosure. I've got the filter set to begin boosting bass.
Here's a EQ curve for the particular settings I was playing around with last night.:
Hz Boost (db)
The boost below 20 Hz isn't much of an issue with digital sources, since there is no rumble to worry about. Any information down that low on DVDs is recorded at fairly low levels, down 30 or 40 dB from digital full scale. As you can see, it works like a standard bass control, except that it is adjustable to be limited to extremely low frequencies, whereas a normal bass control starts boosting at 200 Hz and might be 8 dB up at 50 Hz.
With this type of EQ, it really doesn't matter what driver/sealed box combo you have. As long as you know the Thiel-Small parameters and the box size, you can set the EQ to replace the actual performance characteristics with new target characteristics. The limiting factor is excursion, because you are boosting the signal below say 40 Hz, so you definitely want a driver capable of long linear excursion.
Even though the box is relatively small, I could replace the woofer with a 12 inch driver. Even though the box would be undersized (high-Q tuning), it doesn't matter, because the EQ can easily turn it into a low-Q system.
The only system this EQ wouldn't work with would be a vented enclosure. You could use half of it to increase the damping and turn a high-Q vented system into a low Q system by removing the peak. But, you can't boost bass below the tuning frequency on a vented system or you kill the driver. So for vented systems, a peaking "inverted notch" filter with a lo-cut filter would be more appropriate instead of this kind shelving filter.
I've not used their crossovers, but I would expect them to be similarly high quality. They are all available with Burr-Brown op amps as an upgrade -- I didn't figure the ultra lo-noise op amps would be relevant to this particular application.