I used to use VLC and Media Player Home Cinema (MP-HC) as external players for Kodi/XBMC.
Both of those have their short-comings:
MP-HC: When playing videos at a faster speed, subtitles get out of sync. And sometimes the audio as well, depending on the file.
VLC: Gives me gray screens when playing at a faster speed or fast forwarding on >= 720p files. I tried a bunch of solutions but nothing worked.
Enter PotPlayer. Works fantastically, without the above listed issues!