New Customer- Surround Sound Issues

Hi All- new subscriber here.  15+ year Uverse customer who decided to make the switch.  Love DirectTV Stream so far.  Only issue is sound.  Seems I'm ONLY getting sound through my Front Left/Right speakers.  Nothing from the Center nor rear speakers, regardless of the channel I'm on.  I've read multiple forums, posts and tried several things.  Nothing seems to work.

Equipment and settings are as follows:

• TV- Samsung LED NU7100 Series 4K UHD with HDR
• Receiver- Sony STR DH790
• DirectTV Stream box- Osprey C71KW-400
• HDMI from Osprey to Receiver; HDMI from Receiver to TV
• TV Audio Settings- 
  • Sound Output- Receiver (HDMI)
  • Expert Settings- HDMI Input Audio Format- Bitstream; Digital Output Audio- PCM (my only option;  Dolby Digital is grayed out/can't select)
  • *and in TV General settings I have it set to Anynet+ (HDMI-CEC) under External Device Manager
• Osprey Audio Setting- Surround
• Receiver Setting- Pure Direct, but I've tried all the settings. 

Would appreciate any help our guidance.  Hate to lose my Surround Sound.  I've read where a Roku device can support surround, and we have 2 of those devices, however for our main TV we wanted the Osprey to give my wife a more "Uverse look and feel" related to remote and channel changing experience.

Thank you!