strange thing. i use a mac too (ibook g4/osx 10.4.11), my d2+ was always correctly recognized. appeared as supposed as additional drive in the finder. i don't use itunes, i have my music properly sorted in folders on my backup hdd, so i just moved all stuff over to the d2+. the sdhc-card inside the player was also properly recognized, appeared as supposed as additional drive. it just takes a little patience, my ibook needs some time until player and card in the finder.
a bit more information what exactly happened, which music in which format was on the player before connected to the mac, which version of os x, etc...
in my case cowon d2+ and mac work together as intended, no problems after several months of use.