Basically, at 8th level, you have a +2 bonus from Inspire Courage from your class.
Inspirational Boost, Badge of Valor, and the Song of the Heart feat, all boost it by 1. So +3 total.
A Masterwork Horn boosts accuracy and damage by 1, but imposes a -2 penalty on saves vs fear.
Words of Creation doubles your IC bonus. RAW, it just doubles things. RAI might have been to double the bonus you get from classes, but there's no way of knowing that.
So your new IC bonus for an 8th level bard is either 2*2+3+1 or (2+3+1)*2 which results in a +8 or +12 respectively.