P4R800-VM boot device selection problem

I have just installed a P4R800-VM motherboard with an IDE DVD-ROM drive
as secondary on IDE channel 2 and a SCSI drive on an Adaptec 29160
controller. There is no floppy disk drive. When I go into the BIOS and
go to setup the boot order, I find that I can choose to boot exclusively
from the DVD drive, or I can choose to exclusively boot from the SCSI
drive, but I can't configure a boot order to boot first from the DVD and
then from the SCSI, or vice versa. Only one device shows as a choice - I
can make it the DVD or the SCSI drive but I can't have both there and
set the order.

I then attached a USB floppy drive to one of the USB ports, and with the
floppy attached, all three devices show as boot choices and I can set
them in any order I want. However, as soon as I remove the USB floppy
drive and then go back into the BIOS, I'm back to only having one boot
device available - either the DVD or the SCSI drive, but not both.

Is there any way to fix this? The motherboard has the latest BIOS as
listed on the Asus web site.

Nick