I'm an engineer, but not an antenna engineer or an industry member.
First, I'd say run new wiring for your antenna. Forget trying to use the cable feed. Any splitters that Comcast provides are immediately suspect, because they may block broadcast TV frequencies. Not a preamp.
I suggest you buy a NEW long RG-6 cable. Connect it directly to the TV and whatever antenna you want to try. Run a scan in your living room, in your attic and on the roof, and compare the results. The CV2 is a pretty nice antenna -
https://www.antennasdirect.com/store...V-Antenna.html - look at the technical specs. I would expect it to perform splendidly for you if it were roof mounted, above the trees.
Any splitter will attenuate the signal from the antenna. So will long runs of cable, but not as much as a splitter.
If you bought all these antennas, I think you're basically spending a lot of money on a bunch of roughly equivalent products. Likely they are all operating down at the margins of acceptable signal, and that is magnifying the slight differences between the antennas. If you want better reception, you'll need to go big and go high. The attic installation is severely handicapped from the start, and likely to be disappointing.
Get up in the clear air, above the tops of the trees. Your TVFool report is favorable - you should be able to get a bunch of Memphis stations if you point your antenna N-NW. Likely there is significant attenuation and interference from the building and the surrounding trees.