If you do not have a bigger SSD already the far simpler & easier method is to spend your money on a standard SATA SSD with cloning s/w & instal it in a spare slot in your XPS8900. My system has a single 3.5" 2TB disc and the 2nd HDD slot is empty, the 8900 chassis also comes with the mechanical & electrics where traditionally a 3.5 floppy drive would go. (So why is the Intel RAID system activated with only a single HDD installed Dell?) Some people do seem to have 2 x 1TB HDDsin their system.
This Dell KB link explains how to enable the boot from a DVD, I expect that the same principle will apply to any other SATA based device, you could even instal a SSD in the 2nd DVD Drive slot.https://www.dell.com/support/Article/us/en/04/603195/en
I'm just about to do exactly that - wish me luck!