SD2SNES doesn't support MSU-1 with additional special chip, for example, on Kirbys using SA-1 it won't work either. FX PAK Pro does support both chips.
On the series s/x you can use a external HD but any next gen games must be on your internal ssd, or you can buy a ssd expansion card, but pricey. Any xbone, 360, or og Xbox games can be played from external tho.