Q: cellular internet streams only stereo through lightning port

I am trying to do away with my internet cable.  I want to stream HDX video and surround sound through my MD826am/a

Lightning Digital AV Adapter through a Marrantz surround sound receiver using an HDMI Cable.  While streaming through the Apple Netflx App, I get a good video picture, but only stereo sound PCM and 2.0/0.  When I turn on Wi Fi I get Dolby D 3.2/1.  I'm using Sprint as my cellular service with unlimited data.  They stated that my account has no restrictions on bandwidth and if they did it shouldn't affect audio.  While doing a bandwidth test using Bandwidth.com and Speedtest.com, both show my cellular network at 30-40megs, while my internet through Time Warner Cable registers only 20Megs.  My signal strength registers 2-3 dots.  While using the VUDU Apple App, I can only get stereo sound regardless if I turn on Wi Fi through the AV Adapter.  I'm wondering if the circuitry in the adapter is preventing dolby sound from a cellular network and this may be an iPhone problem.  I am using an iPhone 6s with ios 9.3.5.  Apple Customer Reps have little input being unfamiliar with the AV Adapter.  The Tech Services rep I talked with was not an iPhone specialist and was unable to help either.  Has anyone run into this problem?  Under Music in the settings menu I selected 'Cellular Data' on and 'high quality audio' on.  This didn't help.  I've played the same movies through my blue ray player and have confirmed dolby 3.2/1 for them, so it is not a case where the movie is only broadcast in stereo.