The active bass in this speaker uses a line level active low pass filter, and likely some EQ to achieve the target acoustic response.
Use an acoustic measurement system like omnimic or REW to measure the bass driver’s acoustic output frequency response.
That is your target for the filter you apply to your new external bass amp. Put the microphone very close to the driver while measuring the old filter and leave it in the same place while adjusting the new fiters.
Since you’re essentially starting from scratch in designing the filters you can physically remove the old amp to increase box volume for lower Qts.
The original has speaker-level input to the internal amp.Amps require line level input, so to duplicate that you will also need to design a new attenuation network (high power L-pad) to match the new amplifier’s gain with the sensitivity of the upper range drivers. An external amp with internal DSP would make it easier than replicating the analog line level filters, but will still need LPad unless you supply the bass amp a line level full range signal from your preamp. You might be able to reverse engineer the analog filters from the old PCB to get a head start on analog filter design if you want to stay analog.
Fair warning, this is a significant project, not for speaker desiger neophyte. It will require adjustment of gains and filter curve shapes by ear after initial design.
