I’m slowly diving into a backlog of un-replied questions.
These ink sets require a minimum of 6 channels to work. That being said, Special Edition and Carbon do share some positions. It would be a strange marriage but essentially you would put spec-ed (k6) into the printer and then put carbon shades 3,4,5,6 into the remaining 4 channel slots. This would be a matte only printer and require some re-mapping of the curves which is fairly easy.
tldr: yes, you can put both Carbon and Special Edition into a x900 10 channel printer. It would be a matte only printer.