1620 burning speeds on -r discs

I just got this today and I use -r discs I would like to know how to burn discs at 6 speed I have look at the firmware with media code and see no discs set to burn at 6 speed I tried changing Ritek G05 to 6 speed in Mediacode but I could never get the ext box to unghost I tried a few other -r discs with no luck can anyone help.