Interesting to see that others have had this problem too. In FreeBSD, the cdrecord/mkisofs/etc have had problems in the past detecting the proper speeds of my DVD burner. I had to pass command line arguments to mkisofs via k3b's advanced settings to get burning to work properly.
Like linux, in FreeBSD ATAPI > SCSI emulation is required to burn CD's, only it's looks like it's much simpler to get working. You just load the 'cam' kernel module and go.