For those curious, I've trashed the prefs and it didn't help. I switched back to my original 1.25ghz daughter card and the software recognized the heat sensor. Under the previous card it sound like the fans were randomly slowing spinning up and down, like it didn't know what to do. The original card had the computer run the fans at a more consistent speed.

And for the very curious, it doesn't seem like there's any harm using a dual processor heatsink on a single processor card. It works just fine.