Reading the manual, it appears that it does have dual bios [2 x 32mbit flash and 4MB bios file], but the 2nd one is just backup and not user accessible. If the system detects a bios error, on the next boot it will load the backup and overwrite the main with the backup.
I can only imagine that both bios's are updated in tandem [or one then the other] when you flash to a newer version.