FYI, I outlined the instructions for substituting your own MPV library in this post: HTPC Tips and Tricks - #3 by gbooker02. In there I point the tls-ca-file to the cert in the Plex HTPC install which saves you a step.
Also, note: (At least the last time I tested it) gpu-next with winvk uses software decoding and not hardware decoding.
