I have had really bad luck with the Sub-10. I bought one about 4 years ago and the original amp lasted about 18 months and then it would just buzz. I couldn't find my receipt so I wasn't able to get it fixed under warranty so I ended up buying a replacement amp from PartStore.com or something. It was the Klipsch replacement. I think it was about $120. That lasted about another 18 months and then it died. This time I have sent it in to Klipsch for the 60 dollar repair on the sub-10 amp. That was a few weeks ago and I am still waiting on getting it back. I am considering selling this sub once I get the amp back and trying to find something a little more solid.
As for that amp fitting... the biggest problem will be fitting it to the opening. If you are comfortable with a router, you could make the opening bigger and have the lip fit over it nicely... if not, I would suggest just getting the amp fixed by Klipsch for 60.