I have formatted a DD660 and is prompt for BIOS login credentials. I tried root/sysadmin as login and password as serial number as well as d660d. No luck..
BIOS password for a DD660 is d600d.
The only things that you should change in BIOS would be the boot order to allow the system to boot off of a USB key for a fresh install. Then after installing the OS, you need to put the boot order back to the system default for proper operation.
For default login to a fresh install of DD OS, the login name is sysadmin and the password is either the system serial number or abc123.