I have two different issues, but am posting both in the same thread, since they both relate back to Amazon TV clients...
I have many Plex client devices, including ATV4 (x2), Roku Stick, Android (Nexus 7 FHD x2), iPhone, iPad, and of course Web.
I run a main Plex server on a 2012 Mac Mini w/attached USB3.0 12TB RAID 5 and 8TB RAID 0 Plex Library Drives. All Media is encoded as 1080p, h.264, AAC (Track 1), AC3 (Track 2) in mp4 containers. Some have subtitles (iTunes type files) and others don't (burned in subtitles). This is my main Plex Server, and has been working quite well with all clients, except FireTVv2 and Firestickv2. (I'll get the FireTVv2 issue in a moment...)
For the sake of backup and redundancy, I have a NETGEAR ReadyNAS 2120 40TB that I use to back up the Plex Media Library. That is it's sole purpose...to keep a backup of my Media. Because the ReadyNAS 2120 can also run apps, I have also installed and run a 2nd Plex Server from there. The ARM based ReadyNAS 2120 cannot transcode, and I knew that going in. However, it was my understanding that all of my clients are capable of natively playing MP4, 1080p, h.264, AAC, AC3 without needing to transcode. The idea with the backup was to have Plex availability in case the main Mac Mini 2012 server needed any maintenance, etc. And since the only thing the ReadyNAS 2120 was doing anyway was to backup the Media Library, I figured "what the heck", I'll just run a 2nd Server on the NAS and have a working backup Server. (Syncing the Plex Databases would be awesome, but that is another discussion...)
Well, during Mac Mini defrag maintenance over the past week, we made extensive use of the Plex Server running on the ReadyNAS 2120. Everything worked pretty well (although a bit slower GUI) on all clients except the Firestick TVv2. It would not play our files, without giving the "Server is not powerful enough..." dialog. I tried to search here for some troubleshooting tips, but could not find anything that worked.
The Firestick is about 7 feet, line-of-sight across the room from my AP, and is 5GHz Wi-Fi connection at max PHY Link. All settings on the Firestick Plex client are set to allow direct streaming...and h.264 level is set to 5.0, which is above any of my transcodes. Auto convert in the client is turned off. Quality is set to original. Firestick and AP were both rebooted many times as a troubleshooting measure. Firestick seems to have no issue streaming direct using DLNA, but will not do so from the Plex Client. I would prefer to use the native Plex Client.
Why does the ReadyNAS Plex Server/Firestick combo insist it must transcode to the Firestick, even though I have all the settings implemented for direct play? Why is the Firestick the only device having this issue, while every other client I have (Including TWO 2013 Nexus 7s running Lineage OS ROM and Plex Android client) have no issue running direct-play? In fact, all other clients work beautifully and (except for the Firestick) we were quite pleased with the performance of the backup server while the main server spent a week doing a full defrag of over 11TB of files.
Seem to me there is some issue with the Firestick Plex client, and I would really like to understand why? What is different from the Android client? Is there anyway to fix this?
2nd Issue: Can anybody verify that Plex on Amazon Fire Tv v2 cannot play AC3? I've specifically picked the 2nd AC3 track, but my receiver insists it is still only getting Stereo over HDMI 1.4 cable. I have an Apple TV v4 hooked to the same receiver and AC3 is working correctly from the Plex client on the ATV4. (My receiver is an Onkyo TX-NR809, and (as I say) works great with every other HDMI connected device.).
Appreciate any insights and troubleshooting tips you guys might have. At this point, Amazon devices are mostly useless to me for Plex until I can figure out a fix.