Changed to across..
The voltage between the two driver bases won't change much when you replace R42.
But the current through the drivers will.
Look upon C12 (and all the bias the parts attached to it) as an elevator.
It can rise up and down, almost to the 60th floor and 60 floors down.
But the height of the elevator always stays the same.
A fusable resistor is just a normal resistor that burns up in a controlled way when something is wrong.
Up to you to use fusables or not.
R9 should be 1k. I assume you measured that disconnected, not in circuit.
A wrong value here could upset the balance of the amp.
Leo..