In my poking around before, I saw mention that most MPX players also handled ...some other format...
...and in trying to recall what that other format was, I stumbled over this:
https://web.archive.org/web/20100815084506/http://www.kingston.com/support/PORTABLEMEDIAPLAYER/Transcoder.asp
"The PMP Transcoder is the KPEX100 tool that enables you to convert WMV, ASF, MPG, and AVI video files into the supported MPX format."
Had to download via Curl because Chrome sucks, but it did successfully convert an AVI - hopefully MPX is a single format, and doesn't do player-specific codec stuff or whatever...
EDITED: 18 Jun 2018 19:56 by BOUGHTONP