... then just put 'gp2xsound.wav' on a blank SD, hold Start + Select while booting up the '2X ... it will just update the startup sound, leaving the newer FW. Voila!
Oh, and while you're at it, why don't you do everyone a solid and uplaod it to the archive as "Original GP2X Bootsound" or something like that ... this request pops up every so often