If you haven't already, make sure the High Pass filter is dialed in on those channels. It's probably good to have it as a default, unless you specifically need to go lower then that.. 80hz would be a good place to start, and move up from there..

There might also be a HP filter on the amps.. If you're using ceiling speakers, they probably don't go down that low anyways, and you should set your HP filters appropriately to protect them.