Just ran across a weird problem with my 5K iMac, a miniDP to HDMI adapter, and CEC control on my Vizio P702ui-B3 (previous-generation P-series) TV. The relevant part of my home theater setup is this: iMac > miniDP-HDMI adapter > HDMI5 input on TV (HDMI 2.0 compatible input) TV <> Pioneer Receiver I have CEC enabled on the TV and the receiver, so the TV will feed audio back to the receiver via ARC (in addition to some control stuff). Works just fine. ...unless I plug the HDMI adapter into the iMac. The TV gets video and audio from the computer, as you would expect, but the TV's CEC connection with the stereo fails completely. The TV doesn't even detect the stereo, and it won't pass audio back to the receiver. I'm actually 90% sure I had this working at some point in the past, but it definitely isn't now, and I can't figure out why having something hooked up to one of the HDMI inputs on the TV would have any effect on the CEC connection to the receiver via a different input. I'm guessing that the iMac is trying to pass some CEC signals to the TV as well, but even if that's true it seems like the TV should detect both devices (or at least the iMac first), rather than none at all. Anybody had this happen to them? Suggestions? I kind of want to use the HDMI2.0 input on the TV for the computer instead of running the signal through the receiver, but it's obviously not an option if there's no sound passthrough available.