Regular Feat + Sudden Feat

[BlueBlackRed]

Wohoo! I found it:

SRD:
Multiple Metamagic Feats on a Spell
A spellcaster can apply multiple metamagic feats to a single spell. Changes to its level are cumulative. You can’t apply the same metamagic feat more than once to a single spell.

Thanks rvalle, when you add that to this -
Sudden Empower:
Once per day, you can apply the effect of the Empower Spell feat to any spell you cast without increasing the level of the spell or specially preparing it ahead of time.

Looks to me like the Sudden version is just copying the feat for special circumstances (spontaneous casting).
No stacking.

 

[Nonlethal Force]

I would also go with no stacking. I realize a sudden empowered maximized fireball is more powerful than a sudden empowered empowered fireball ... but the intent of the rule is that the same effect doesn't stack. Since Sudden applies the same effect as the regular feat ... no stacking.

This is an analogy with many holes, but it is like MWK versus a +1 enhancement. For a little money, you can get a +1 to attack through MWK weaponry. But through more money you can get an enhancement to attack and damage. The two don't stack. [I know, it has many holes as an analogy. I admit it. Please don't feel the need to shoot holes in it.]