I'm wondering if a BIOS flash is necessary to get a large HDD working properly.
Possibly, but I don't know.
My version is 1.09 and I installed a dual-boot but for some reason one of the OS' will not load. I also get a message before my linux boots that a forced ACPI will be done. It also says something about an old BIOS image (1999) and no (2000) BIOS. Something along those lines.
Note that the internal BIOS date of ALL 600X BIOSes is 1999, even though the release date for some of them was a few years later. The reason for this has to do with something about Windows 98 installation and the use of the BIOS date to determine ACPI/APM compatibility.
I'm not saying you shouldn't upgrade your BIOS, and maybe that will solve your problem. I'm just noting that you should be careful if you are relying on the internally reported BIOS date to make any decisions about this.