Nu saxar jag bara in ett svar jag hittade efter google sökning.. Men det kan ju vara värt o prova om det hjälper dig iallfall
"Another thing that may work to get subtitles working in MPC-HC is to make sure you are using the "EVR custom pres." renderer in Options, Playback, Output. Not all renderers work with subtitles in MPC but this one does."