I thought I'd share a couple of observations that may help others.
1. Last evening, I temporarily installed an HDTV antenna in our living room.
Without question - in the SF Bay Area / Silicon Valley - Over the Air (OTA) TV is superior to Comcast X1 service. (I know - low bar - so, I may look at moving over to Direct TV and using OTA with DTV).
2. This afternoon, I plugged the Z9D into a Richard Gray Power Company RGPC 400 line purifier.
This immediately improved both the Comcast and the OTA picture - a lot less noise. I have a larger one on order for the AVR/Amps/etc., and I'll be curious to see what, if any effect is has on sound and other picture quality (like blu ray and external streamers).
I think with these two things (OTA & Power Conditioning) everyone's mileage may very, depending on source and circumstance. However, they both improved my experience instantly and noticeably.
Dolby Atmos 5.1.4 - Revel M126Be's, C205, M106's - Rythmik F12SE - Revel C763L's
Marantz 8805 - Rotel RMB 1095 and RMB 1075
Sony 75 Z9D - Sony UBP X800M2
Pioneer KRP-600 with Heos SoundBar 2.1