If I remove the 1.5µF cap (doesn't seem necessary) Put 22 ohms across the piezo and add a 15 ohm in series with the parallel leg of the 8 ohm L-pad and push the x-o frequency up to 4500 calculated on 16 ohms (2.2µF), The R1 resistor would be set for the half way position on the L-pad, giving partial cut and gain. (I know that it would not give the same dB cut as on the face-plate of the L-pad, but I wasn't planning to use it anyway.)
Do you reckon it would work ok?

My calcs seem to indicate that the resistance seen by the x-o capacitor would vary between 15.2 and 16.9 ohms. This is probably quite a bit more stable than a normal driver.