25 supplys at 6" apiece adds up to (28" x 25= 700 inches of air. But the main is only 8x20= 160 inches. That means the MAIN DUCT is much TOO SMALL to handle this amount of supply takeoffs.
You need a pro to come in and size the supply AND return properly.
I have already had 4 supposed pro's out here, I cant afford anymore pro service calls!! That's why Im here. Do you think if I had the money I would come to a forum for help?? Everyone I had out here said everything was fine, what a waste of my money.