Well, it seems you've done the diagnostic work for the technician yourself - it worked fine until you hooked up the center channel. That pretty much says it all. Dropped or not, the unit worked before hooking up the center channel. As I said in my previous post, "honestly evaluated". It doesn't seem as though you've made it to the 'honesty' part yet. Find a new technician, and by all means, DO NOT spend more than $125 repairing this unit; it's not worth it. Honestly.
-Richard
-Richard