Optimal replacement 8" drivers for M&K MX700 subwoofer

Replacement woofers for MX700 subwoofer

I have 3 of them and I'm thinking of experimenting on 1 of them since the plate amp is malfunctioning.

Currently using a Crown xls2502 configured in bridge mono and 85hz low pass to replace the plate amp. Cut the + and - and pig tied them to some speaker wire and connected the amp. Works.

Now I'm thinking what would be the highest performance 8" speaker driver to replace the existing M&K 8" drivers? How to I select the drivers based on the push pull configuration?

I'm looking for very fast and clean bass down to 20ish hz. They would need to run without too much heat as I often listen for hours at a time, albeit not at super high db levels.

I have a few Crown and other pro amps lying around and really like the form factor of the MX700 so when those plate amps die, I have a solution.
Thoughts?
Thanks in advance.