Hi Dan,
The Apple support article I linked to says that AppleTV 4K only has an issue playing hi-res lossless at sample rates greater than 48 kHz. It doesn't mention using an external DAC, so that's probably not an option.

When using an Android device, the article also mentions "To listen to songs at sample rates higher than 48 kHz, you might need an external digital-to-analog converter.*

*To see if your Android device requires an external digital-to-analog converter, check with your device's manufacturer.".

That seems to be consistent with whqt you saw.

Thanks,

Jim