I want an optimal result on the TV.
Well, don't we all? 
I could be wrong, but I don't think that HDR support is already incorporated in Kodi. The Nvidia Shield can do it, but that's an Android box. Also VP9 support is not on every hardware's list I think. So you may have to make a few concessions.
Try this list first: START HERE - Pick the Right Kodi Box (updated May 2017)
S905D are the chips to watch for (devices with them should start to appear soon) as they have the same spec as S905X but with GB Ethernet. There is no HDR support in Linux at the current time but the first patches for HDR support on Intel GPU's were submitted to the Linux kernel last week so that will change in the future. Once things are in-kernel Kodi can start to evolve support. Once Amlogic completes work on a mainline kernel (not the ancient crap we are using today) support can be added there too. Android is a completely different discussion and I'm honestly not aware how good/bad things are there. It's usually a hack-fest of bad though.
