So to follow up on this post, I ended up getting the 976 preamp and swapped the 975 out. Plus all new cables rated for 4k. Problem solved.
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My system:
Outlaw 976 receiver
Wyred 4 Sound Mini MC5 5-channel amp
Vizio 75" P75-C1 4k display
Currently 3.0 surround with 51" Martin Logan ESL for L/R, Martin Logan Motif-X for Center (will do full 5.1 eventually, just haven't had time yet)
Apple TV 4k
Oppo BDP-103 Blu Ray
TiVo Series 4
PS4
Motorola QIP7232 2 Cable Box