Ensure that you are not running Media player or any other audio programs simultaneously with Studio One. This can cause a conflict with the interface as to which program to utilize and which audio signal is outputted....hence the use of the exclusive mode.
Additionally, playing a file through media player will not direct it into Studio One. In this case when you play the file, you are utilizing the outputs of the interface, not the inputs. It is possible to import a sound file directly into Studio One, or you could utilize an additional computer to play back the audio into the interface inputs and record those sound files manually.
Hope that helps!