I 'm sorry to hear about the dead amp, but the fix is simple, convert the unit to be a passive sub (no integrated amp) and get a suitable external amp to drive it.
I have done that with a couple of secondary system subs, and it works fine. A sub is a pretty simple beast.
I assume the Descent woofers are wired in a specific fashion that has only two wires connecting them to the Amp module, correct?
A pic of the wiring (or a schematic) would answer that.
So once you figure out the wiring, powering it is simple; just identify an amp with the juice to drive them well. I have some thoughts on that.
But physically, you'll need to block off the hole where the amp goes, or leave the plate amp in place as a physical barrier, and run a cable out through a new hole to connect the woofers to the amp.
Do you use any of the crossover functions in the sub itself? Or is it a more traditional LFE in where the crossover, levels, etc. are all set in the upstream processor?
Assuming the later (and you should be doing that), then the amp can be pretty straightforward. For sub-duties, class D amps are the primary choice as they can put out the watts in a highly efficient way.
My preference, possibly due to having all my gear in a sperate equipment room, and therefore invisible, is to use pro-audio amps from the likes of Crown to drive subs. Crown amps are quite robust and are available in a wide, wide range of options and power levels.
For sub duties, I like the Crown XLS series, with the 2502 being what I would recommend for a Depth:
https://www.crownaudio.com/en/product_families/xls-drivecore-2-series
I run an older Crown 2500 pushing a Dayton Ultimax 18" driver in a re-used Velodyne ULD-18 enclosure. So I've been down this path.
