The interface can handle unbalanced signals. I know almost synths are unbalanced, and it hasn't had problems with any others before this. According to the manual:
The analog line inputs of the Babyface can be used with +4 dBu and -10 dBV signals. The electronic input stage can handle balanced (XLR, TRS jacks) and unbalanced (TS jacks) input sig- nals correctly.