Connect the audio interface to your computer using the firewire cable. Audio interface devices like the PreSonus FireStudio act as an intermediary between external audio devices such as mixers and microphones and computer software workstations. If you do not own an audio interface, you can purchase one of these devices from popular audio equipment stores such as Guitar Center. Ensure that the audio interface you purchase has multiple XLR inputs.
Connect the Behringer mixer to the interface using the two XLR cables. Plug the cables into the two XLR "main outputs" on the back of the mixer and two XLR inputs on the audio interface. Power on the mixer and audio interface.
Launch Cubase and create two new "audio" tracks. Open the "settings" menu within Cubase and select the audio interface as the primary audio input device. Configure each track to receive audio from one of the XLR inputs on the interface. As each input on the interface is numbered, select the appropriate number within the "input" settings menu on the audio track.
Press "record" within Cubase to begin transferring audio received by the mixer into Cubase. Any audio from instruments or microphones you have connected to the mixing board will now be transferred directly into Cubase.