The predicted signal strength from your TVF report argues against using any amplification.
WCOO-FM 105.5 shows up in the same area, the 5th harmonic would land in the middle of UHF CH-23... not CH-24. If this were an interference problem, I would expect video to break up also. So.... Hmmm?
Still you could through an FM trap in the line just to see what happens.
http://www.antennasdirect.com/store/...on_filter.html
Audio is now sent in mono, stereo, Dolby Stereo, 5.1 and I'm probably missing a few other formats. If Fox is using one of the higher performance audio formats 5.1 for example, are any other broadcasters using that format and are you experiencing any trouble with their audio. (I'm wondering if your set may have a problem staying locked in when receiving the audio format used by WTAT) Try searching online using the model number of your set and the phrase 'audio break up' or 'audio drop out'