Just remember, in most cases, the furnace was not sized to maintain temperature in the basement. By adding vents. you reduce the heating / cooling air supply to the main house. If you have insulated the basement walls real well, what you have should be OK. The only way to do this correctly is to install a zone system. They are not worth it for a small area unless you have money to burn. I personally would not install any registers in the mechanical area of the basement.