Ok i know things like Ibuki4, iga legacy, etc all feed into hunger for souls. But lets say you check a 2 and commit foundations to pass the check, do you destroy 2 or 4 foundations?

I.e. does commiting foundations to pass a check actually INCREASE the control check, or just keep it from failing?

Just keeps it from failing. Cards that modify (+ or - to a check) such as Iga legacy will alter the number of cards destroyed by Hunger for Souls. In your case, if you check a 2 and commit cards to pass the enhance only two cards will be destroyed if the attack goes through.

This question is also relevant to Cervantes' 2nd R:

"R (3+) Commit: Before your opponent makes a control check, that check equals the check you made for this ability. Failing that check will not end your opponent's Combat Phase."

So if you check as the cost to play this ability, and you check a 1, then you commit 2 foundations to make the check successful, your opponent's check becomes a 1.

stamps ahoy.