Here's my setup: the thunderbolt 2 port on my mac is connected to a mini displayport to hdmi 2.0 adapter, which connects to an hdmi cable that goes into a tv. The tv passes the audio through a toslink cable to a stereo amplifier, and then the signal goes through speaker wires to my speakers. this setup has worked flawlessly up until today. For some reason, mini displayport is only carrying audio when set to 4k 30hz or 1080p 60hz, but not 4k 60hz. This has dumbfounded me. I've switched the hdmi cable out, messed with SwitchResX and audio midi setup settings, and even downgraded from the high sierra beta, with no success. I've restarted and unplugged all aspects in my setup, with no avail. I have no clue how the hell this happened. Now the only way I can get audio through my speakers from my computer is through my echo dot or a aux cable.