Connect a MIDI-compatible external sound card to any available USB port on your computer. You have two basic options. You can connect a USB audio interface (available at music supply stores), which looks like a mixer or a small box containing different audio jacks for guitars, microphones and other instrumentation, or you can connect a more inexpensive MIDI-to-USB adapter, which looks like a cable with a small box attached to the end (containing MIDI ports).
Connect a MIDI cable to the "MIDI Out" port along the back of your MM6, and connect the opposing end of the cable to the "MIDI In" port on your interface or adapter.
Open Cubase LE on your computer and click the "Devices" menu along the top of your screen. From the drop down list, select "Device Setup."
Click "VST Audiosystem" in the left column of your "Device Setup" window. When the "Input" menu appears, select your USB interface from the list. If connecting with a simple MIDI-to-USB converter cable, Cubase should pick up the device automatically, in which case you can skip this step.
Create a MIDI track, which allows you to record digital instrumentation from your MM6 to your computer. The "track" is simply a long horizontal bar, on which your recorded material will appear, like a musical layer. To create a MIDI track, click the "Project" menu at the top of your screen, hover your mouse over the "Add Track" option (appearing at the top of drop down list) and select "MIDI." The track will immediately appear on your project window.
Assign a virtual instrument sound to your MIDI track. Your MM6 functions in Cubase as a MIDI controller, meaning that you can select any virtual instrument from the Cubase sound library (including keyboards, synthesizers, bass, brass and drums) and use your MM6 to play the sounds in real time. Click the track once with your mouse to highlight it, click the "Devices" menu at the top of your screen and select "VST Instruments." When the instrument menu appears, select a virtual instrument with your mouse.
Click the red "Record" button at the top of your project window and begin playing the keys on your MM6 to record music in real time. When you finish recording, press "Record" a second time to stop. You can add as many layers of music as you want by simply creating new tracks and assigning a different instrument to each one.
Save your project. Click the "File" menu at the top of your screen and choose the "Save" option.