Holy crap they must have been very over tightened! That will warp the rotors in no time.
Be careful using a breaker bar. Using a lot of force with a breaker bar puts a lot of force downwards on the bolts and can damage them. Using an impact will only put pure rotational force on them and is much safer.
May be time to get a better impact gun? At home I use a Snap On 18V cordless impact. Have never had a nut/bolt that thing will not take off.
http://www.motherofallcordlessimpactwrenches.com/
And if that does not work, I have an 800 lb.ft air gun at work.