Different cable boxes handle the scaling differently, and upscaling in cable boxes often is not the best. Check to see if yours have an "original resolution" setting so you can avoid upscaling SD resolution signals to HD in the cable boxes. Alternatively, setting them to a fixed 1080i is a reasonable compromise, if only because that will let the display devices do the upscaling to 1080p for HD channels.
Many people have encountered problems when sending high bitrate signals through a long HDMI cable, like to a projector. As a result, you should minimize the bitrate by making sure that "deep color" is disabled in your Oppo Blu-ray player. No video source material available to consumers has more than 8 bits/color channel, so enabling "deep color" increases the bitrate unnecessarily.
Marantz SR7009+MM9000/Atmos 7.1.4 (FH+TM:DefTech PM1000)/LCR+TM amped