I had the amp from my 2006 DD18 repaired just in the last few weeks. I used "the amp man" who you can find on ebay. I was somewhat surprised it could still be fixed but I had it back in about a week and couldn't be happier. Total cost to me was around $400 including shipping. I really don't think it gets much better than this if you're using it at true subwoofer range. Plenty of output and the servo means no distortion. I was eyeballing SVS before I decided to see if it could be fixed and I'm glad I got it fixed. There's no way a 13 inch sub with half the surface area could compare.
Amp man directs you to a video showing how to remove the plate amp in the description. Disconnecting is easy, take a few pictures before disconnecting the wires for when you're reconnecting. No cutting or soldering required.
Velodyne Subwoofer Repair Service DD Series (authorized service center) | eBay