I've been lookins the specs of Cowon Q5W and noticed it has built-in Flash7 support. As far as i know the latest Flash for MIPS is 5.
By the way it has MIPS2 core... I can't say anything. Maybe there's nothing to do.
Still, here's the link to the latest firmware (bin included). http://www.cowonglobal.com/download/Firmware/cowonQ5W/1_51/COWON_Q5W_1.51(20080911)_FW_ENG.zip
I guess it is all on how they coded the player. Code compiled and/or linked using the -mips2 option will not run on R2000/R3000 based machines. Code compiled without the -mips2 option will run on all machines. Now someone need to figure out how to turn the bin files into executeable programs...