3.5 Stacking Criticals

[Pyrox]

So going through some of his books, a player in my game decided he wants to be a mounted fighter with a lance. Going through the rules myself I found that:
1) the lance gives you a x2 multiplier on damage when mounted,
2) a lance has a x3 critical, and
3) Spirited Charge gives you a x3 multiplier when mounted and charging.
I don't necessarily have too much of a problem with this as there isn't as many random encounters as there are dungeons and street fights, I really just don't know how they stack, or if they stack at all. Any advice would be appreciated.

[BRC]

So going through some of his books, a player in my game decided he wants to be a mounted fighter with a lance. Going through the rules myself I found that:
1) the lance gives you a x2 multiplier on damage when mounted,
2) a lance has a x3 critical, and
3) Spirited Charge gives you a x3 multiplier when mounted and charging.
I don't necessarily have too much of a problem with this as there isn't as many random encounters as there are dungeons and street fights, I really just don't know how they stack, or if they stack at all. Any advice would be appreciated.

As I read it, Spirited Charge+Lance overrides the Lance's multiplier, since it specifically says

Benefit:
When mounted and using the charge action, you deal double damage with a melee weapon (or triple damage with a lance).

I take this to read "You deal Triple damage instead of the double damage you would normally deal".

The Spirited Charge+Crit definetally stacks though, so a critical with a sprited charge lance would deal x6 damage.

Of course, that depends whether the equation is
Damagex3(Charge)+Damagex3 (Crit) or (Damagex3)x3.

[Myrmex]

Two doubling equal a tripling with D&D math, but they explicitly spell it out for you with lances & spirited charge.

A lance doubles your damage, and a spirited charge doubles your damage, for x3 damage total. If you critical on that charge, you do x5 damage.