Catastrophe averted. I pulled the amp out of the rack and was able to easily remove the broken off screw. It came right out. Swapped out the post on the 2 ohm tap and reconnected everything. It's working fine.
Will be calling Mc early next week to order a couple extra posts. Seems the metallurgy is gold plate over cast alumium. It's pretty brittle although I admit to over-tightening it.
Man, I did not need this on Christmas Eve.
