Dual-Driver small Subwoofer - immitate a passive membrane by DSP delaying?

Hello
im a big fan of Sunfire subwoofers, i myself got two XTEQ 10. they are using a active and a passive 10 inch chassis and can get quite low for its size of 32cm cubed.

Now i got hold of some B&W LF03077 for almost free that are found in the B&W DB2D subwoofers with carbon fiber membranes,

i built myself a sealed Box with almost the same dimensions of a DB2D using 22mm MDF and two of those Chassis.
IMG_20240204_120405.jpg
original DB2D looks like this on the inside, having a huge class-d amp below.
1707048133249.png


But the resonance is at 35hz, higher than the original and its efficiency seems quite low.
And below 20hz it drops off a lot.

now my question is
would it be possible and if yes, how to delay/phase adjust one driver to immitate a passive radiator of some sort (prefferably with DSP or something)
or is there a better way to improve it other than a bigger box?

i got some experience in sigmastudio dsp stuff and a adau1701 board laying around somewhere if could find it.