Hey guys, I am in the same situation. I have found two other threads on the issue. It is definitely not an HDMI issue or a WiFi issue. Someone has tried to fool the app on what device it's on and it worked but it was too much work. There must be a simpler way to achieve this.
I would love to see someone figure this out. I have tried to tinker, but I am just not smart enough to make it happen. Hopefully one of the many crazy smart dev's will take a look at this sometime. ((fingers crossed))
What is the exact error that you are receiving? I use to be able sideload a Direct TV apk for either the phone or the tablet but now they have stop working. When it worked fine it was amazing. I was able to watch my subscribed premiums. I think we need to incentivize developers to find a means of allowing functionality through our Nvidia Shield. I will pledge a 300 bounty for the first person that finds a work around. There are many gifted people on this forum and as a whole we can solve this issue.
I got mine working. I did a Sideload APK install from APK Mirror "DIRECTV for Tablets 4.7.015 by DIRECTV, LLC --- September 9, 2016" (select that version)
My problem was that I kept trying to use the Telephone version of this App. I did not know that DirecTv has a Tablet APK version as well that is very similar but has slight variations for older tablets. Let me know if yours works now. I don't need $300, but a $10 Starbucks gift card will do...
*** SINCE I am new to this forum I cant post the link *** Go to the APKMIRROR website and search "Directv" -> then select-> "DIRECTV for Tablets 4.7.015"