I've had the T2 for a while now and have had the same problem watching movies in HD. I'm running it on iMac 10.12.4 and EyeTV 3.6.9 (7517). Most movies on the BBC, ITV and Channel 4 HD channels have music and sound effects but no voice sound. It's not a problem watching older movies (? pre surround sound) or watching movies on Channel 5 HD. I've recently updated to EyeTv 3.6.9 (7517) but the problem still exists.
To export movies for Apple TV I've been using Elgato Turbo.264 HD. To export a file "show in finder" and "open package contents" then drag the .mpg file into Turbo.
