Thanks for that info. Yes, the Atom D510 will shovel the data nicely but in the PMS context it’s grossly under powered. As you’ve seen, then the transcoder gets involved, the eggs tumble from the basket quickly.
Regarding the HP… The Gen8 won’t do HEVC transcoding. You might be able to get it to decode 8-bit (non HDR) but it definitely will not decode HDR. It can only muster 4427 Passmarks. I have an i7-3740 (8000 Passmarks) and it can’t touch HEVC HDR.
For you, decoding the HEVC input, pushing the video stream unaltered and transcoding the audio (while trivial with the xeon), is on the edge of what it might be able do. Remember, it was launched in 2012. The model itself is 6 years old now and the processor even older.
My personal opinion it to step away from those older machines if you want HEVC capability at any level. 4K is extremely demanding and the first Intel chip capable of hardware decoding 8 bit HEVC is the SkyLake platform. Xeons don’t have GPUs. Now, should you locate a 8+ core xeon, you can probably muscle your way through it with software decode but I have no experience with it.