Only Plug Microphones in to the XLR Inputs. Plugging in Line Level or Instrument Level signals via XLR will cause these to enter the Mic Pre. The Mic Pre is not designed to accept these levels and doing so could produce poor quality sound, distortion or in some cases damage the units. 48V Phantom Power should NEVER be applied to any Line or Instrument level outputs and can damage both the Focusrite and other units. XLR connections and Phantom Power are ONLY for use with a Microphone. Always check that your Microphone is save for use with Phantom Power before applying as some Ribbon Mics can also be damaged by Phantom Power.
*DI Boxes can also be used as they are designed to lower an Instrument Level signal to a Microphone Level.*