6 piezo flat array, and a Beta 10 with filters as in the plans (complete with hand wound inductors).
Used with my bass running a Warwick profet 3.2 I can report the following:
The Jack has better mid / high end response that my old 4x10.

The Jack has better low end response than my old 1x15.

The Jack is louder than the pair of them put together.

Thanks Bill, and everybody else from the forum who helped with advice & encouragement.