The headband of vast inteligence (HoVI)grants the wearer an enhancement bonus to Intelligence of +2, +4, or +6. Treat this as a temporary ability bonus for the first 24 hours the headband is worn.
So after 24 hours the enhancement bonus becomes permanent as long as the headband is worn, correct?
So...would it still be considered an enhancement bonus to the stat?
Would a subject wearing a HoVI +4 be affected by Fox's Cunning (+4 to INT) at all?
Would he effectively get +8 to INT?
No, they don't stack. Even after 24 hours, the headband still grants an enhancement bonus, just a permanent one instead of a temporary one.