@Selden Ball: I seem to be good. I have a Mono Price 6 ft Premium certified cable on my UBP-X800 for video, and a standard Ultra High speed cable out of the dedicated audio HDMI port to sound bar without issues. Being able to split the signals unlike the BDP-s6700 which only has one port is nice. It also simplifies things by allowing me to stick the BDP-S6700 on a tv that only supports HDMI 1.4 at most. Devices such as my Apple TV 4 connected to the 4k TV seems to work well with the cable I'm using, the other devices such as the chromeCast Ultra, and RokU stick both have the HDMI connection built into the device.If you aren't having signalling problems (audio and/or video dropouts, "sparklies" in the video signal, etc.) then you don't need to upgrade the HDMI cables, but quite a few people have reported audio and video problems having been fixed by upgrading them.
While logically they shouldn't be required, Certified Premium cables don't degrade signals as badly as High or Standard Speed cables do, so even lower bandwidth signals can benefit. Longer cables degrade signals more than shorter cables do, so they benefit even more.
HDMI is an abomination.
The only wonky behavior I've had, is the fact the TV only seems to be able to handle only 3 active CEC devices at a time out of the four ports. I've tried to kill as much of the android smart interface as much as possible so I can use the TV as a dumb TV, with the smart devices being external, but there is only so much that can be done to kill the built in smart features.