ok. overlooked that. seeing the gpu, I thought the htpc is to serve dual-purpose of movie-music plus gaming. I had assembled mine with that motive, to use it to play older games too.
I don't have a HTPC per say, but I use my PC for any movie watching. I use Media Player Classic Black edition with madVR. All 10bit x265 movies play smoothly.
PC is powered by a Ryzen 2600 with video output from a R9 290 and sound from Xonar DX via S/Pdif to a budget Sony home theatre.
Planning to get a 4k 10bit TV soon