I would replace the plate amp. There are many plate amp options out there. Parts Express has a good selection. No need for a very high-end amp on a sub. I seriously doubt you'll hear a difference. Concentrate on the inputs, power rating and features you want on it instead. If the opening size is different, you can cut out the existing hole to match and if too large you can just add a piece of plywood or particle board over the existing hole opening, paint it and fit the new plate amp!
Velodyne DD15 - worth repairing the plate amp?
The amp in my 2008 Velodyne DD15 is dead as a door nail.
How good is this old marvel compared to today's offerings?
Worth investing another $500 (to have amp repaired, incl roundtrip shipping, tax, etc)? Or just use as passive sub?
How does it compete to modern subs, for example SBS SB-2000 or SB-3000 (both under $1k pre owned)?