Back when I last experimented with Flux Player and Flux Studio, I seem to recall their website still contained references to the player being open source. The source code in CVS at the sourceforge project was however three to four years out of date but there was an archived snapshot of a more recent release (fluxsrc-2006-07-09.zip) which is still available here and other places.
Now unless I am mistaken, all such references to it being open source are gone from the main Media Machines web pages. There are references in various other places to a later source code release from this year but all the files have been deleted from the sourceforge project.
It is still possible to find the deleted files if you google for the file names and substitute them into the standard sourceforge download paths:
Given the four year old age of the files checked into CVS I wonder whether it was released based on an initial open source faith which waned in the face of reality or from buying into the false promise of there being volunteers who would pop up and help out.