This sounds like a system settings issue on your Apple TV. The Apple TV should be able to pass through AC3 audio via HDMI.
I have my Roku Premiere+ Model 4630 directly connected to my HDTV via HDMI and it passes through AC3 audio to the HDTV. In the Audio settings on the Roku you can set the HDMI to “Stereo” or “Dolby Digital (DD)”. Roku models cannot decode AC3 audio to PCM so when you set the system Audio settings to Stereo, the Tablo app just tells you the Roku cannot playback the recording for example.