i would not advise placing the two speices together, genarelly softshell turtles are very agressive. Once i tried housing a hatchling softie and a snapper together and believe it or not the softshell was very aggresive. Also as i recall matamatas need a relitivley high ph level in there cage to survive and softshels need there water very clean. There are many other reasons why they are uncompatiple. please don't try it