You must have a really high end audio system to be able to tell the difference.
The OP didn't specify if the TV was connected to the receiver via optical which may have reduced to sound to DD 2.0. Having a 5.1 AVR can provide a noticeable difference between 5.1 and 2.0. My TV doesn't support DD+ but will pass DD 5.1. A lot depends how the audio is supplied by the content also. That said, I always choose my old Roamio for Amazon over my TV, but there's no difference with a Roku or Blu-ray.You must have a really high end audio system to be able to tell the difference.