I have been having this problem for months! Mine has been limited to two channels breaking up. They have rerun the cable from the tap in the backyard to the house and replaced all bnc connectors and splitters to their brand-no joy!
Just today I replaced my HDMI cables with component cables and an optical audio cable. Still breaking up.
I am supposed to get a new box next week (8300HD). From the sounds of it, it won't fix it either. If, after the last ditch effort with the new box, I still don't receive these two channels correctly, I am cancelling and signing with with Verizon. I have done everything I know to do and they just don't seem to be too interested in fixing teh problem. As an aside, I am the last man standing on our street. Everyone else has moved to Verizon!