Multipliers are additive in Pathfinder because each is a multiplier of the original damage.
Lance = x2 on a charge
Lance + Spirited Charge = x3 on a charge
Lance Critical = x4 on a charge
Lance + Spirited Charge critical = x5 on a charge
How it works:
x1 (base) +x1(charge multiplier) +x1 (spirited charge multiplier) +x2 (critical multiplier).
Add up all multipliers that apply and that is the multiplier you currently have.
How it works (for small) if you critical on a spirited charge using a lance:
In terms of damage dice: 1d6(base) +1d6(charge multiplier) +1d6(spirited charge multiplier) +2d6 (critical multiplier)
Note: assume all 1d6 actually = 1d6+bonuses. I just didnt want to write that each time.
- Gauss