I attack felix faust w/ Ultra Humanite (7). Felix faust stuns, and UH and FF's triggered abilites go on the chain. Which resolves first, and even if UH's controller gains control of FF can the owner of FF still use the effect?
Thanks.

since you're attacking, you're the primary player and your effects will go on the chain first.

so, in short, your opponent will have a chance to KO his Faust before you get a chance to steal him.

EDIT: maybe that wasn't exactly clear.
Faust stuns, triggering your Ultra-Humanite's "steal Faust" and your opponent's "KO Faust to get guys out of the KO pile".
so, the chain looks like:

1 - Ultra-Humanite
2 - Faust

after both players pass, Faust's ability will resolve and he can be KO'd to his own ability...
when both players pass again, if Faust is still in play, you can steal him (or get nothing, if he was KO'd)