Amazon Original Series in Stereo Only

Is anyone else having this issue? Movies I watch on Amazon via the Apple TV are coming they in 5.1. But all the Amazon Original series I’ve watched are only coming through in Stereo. Right now I’m watching the series Brittania and it’s in Stereo. The new series Electric Dreams is also in stereo. Yet if I watch the same series via my PS3 they come through in 5.1. So this sounds like an Apple problem but I don’t know.

Thanks for any thoughts.