Only for information I managed to install a fresh DX4000 Sentinel starting from 4.0Tb WD40EFRX red drives. As usual the whitelist file had to modified both on the memory sticks (recreate and recovery) as well as on the virtual DVD. The only minor drawback: I did not manage to recreate the RAID from 4 drives directly, the DX4000 got stuck somewhere. With two drives the RAID create did work. Of course expanding to 4 drives in this way will need extratime for the migration after the W2008 installation will be completed. Next step maybe will be to see whether a 6 Tb red drive fresh install will work even if I have some doubt due to the very old Intel Raid version on board this NAS.
I remin the WD RED drives not only are still available, as far as I know, but they have much better thermal management and they are significantly cooler with respect to the original enterprise drives the DX4000 was shipped with.