Power Attack



I'm wondering how everyone is playing power attack when it comes to 2 handed weapons. We were playing that a characer with a Base attack of +6 could lower his attack roll by 6 and add 12 to his damage. What made me think this might be wrong was when I read the test for the Monster Slayer feat. The last line reads "The total damage bonus gained may not exceed you Base Attack Bonus" I check this with Rulesmasters who said that the base attack +6 guy could lower his attack by only 2 as this would give him a damage bonus of 6, equal to his base attack.
Is this how I should be playing regular power attack as well?
I think it means the following for your +6 Base Attack character. If fighting a monster, you can:

+0 attack but +12 damage (power attack); or
+4 attack but +6 damage (monster slayer)...

I wonder if you can use both feats and, after using the Monster Slayer, use power attack on the remaining +4 of BAB to get a +0 attack, but +14 damage...