Also, I found this. I have no idea how gear '1', direct drive, wouldn't be working. But gears 2,3,5 use "a" or "c" in combo.
1st gear: direct drive
2nd gear: stage C (130%)
3rd gear: stage A (148%)
4th gear: stage B (169%)
5th gear: stages A & C
6th gear: stages B & C
7th gear: stages A & B
8th gear: stages A & B & C, 325% overall