feats for Supernatural abilities?

[jdizzlean]

are there any feats that replicate things like metamagic for (Su) abilities?

can you maximize a Su?
can you extend a Su?
god forbid, can you twin a Su?

[Saintheart]

Yes. Tome of Magic contains Empower, Enlarge, and Extend (Su) abilities.

Complete Arcane has a smattering of similar metamagic for spell-like abilities: Heighten and Maximise (Sp).

Indirectly, as dragon breath is a (Su) ability, metabreath feats out of the Draconomicon are metamagic on a (Su), albeit they impose longer recharge times in each case.