With so many strong signals & an attic mounted antenna, I can only imagine how much multipath interference the antenna is encountering. A small channel 7-51 antenna mounted
outside would be my first move to help tame the signal reflections. I would also suggest an
FM/VHF-LO trap to help relieve some of the unnecessary RF seen by the tuners.
Splitting the signal 4 ways shouldn't require an amp & will likely make things worse. A clean
stable signal is the key to DTV reliability.