I have basically the same setup you have.... the HD TV, (of course), my Receiver, my speakers (8), and connected to the receiver I have an AppleTV, a Fire Stick, and a DVD Player.

Funny thing about my receiver... and this was the same with my old receiver, (replaced maybe 9 months ago)... using the "AUDYSSEY" setup mic and programming in the receiver I could NEVER get good sound. ALWAYS the voices, (center speaker), would result in extremely muffled and bass'y sound. I eventually nixed the Audyssey setup altogether and went to manual... then over the course of several weeks I kept fine-tuning it until.... welll....

I still don't have it like I want it but it's close. For the most part I can hear and understand the voices now unless, of course, the actors are mumbling or whispering. Which leads too....

These days I often turn on closed-captioning so I can read the dialogue.... I got SICK of rewinding a dozen times trying to figure out what was being said.