Stereo upmix and receiver?

If I’m piping the output from my Raspberry Pi over HDMI to my receiver (set up for passthrough, receiver can decode AC3, DTS etc.), should I enable “stereo upmix” for a music file with stereo to try to get output to my 5.1 setup or should I just do “multi stereo” on the receiver instead?

This seems to explain
http://forum.kodi.tv/showthread.php?tid=193078&pid=1690791#pid1690791