The MPC Studio is a USB control surface, and external USB-MIDI interface, for MPC Software.
You plug MIDI out of the MIDI keyboard into a MIDI input on a MIDI interface that is connected to the computer. That can be the Fast Track Pro MIDI input, the MPC Studio MIDI input, or the input on any other MIDI interface connected to, and working with, your computer.
If your MIDI keyboard has a built-in USB-MIDI interface, you can connect it to the computer with a USB cable, instead of into the Fast Track Pro MIDI input with a MIDI cable.
The Virus Snow has both a MIDI input and a built in USB-MIDI interface, so you can connect it to the computer with a MIDI cable, from a MIDI output on a MIDI interface that is connected to the computer, such as the Fast Track Pro MIDI output, or the MPC Studio MIDI output, or the output on any other MIDI interface connected to, and working with your computer.
You can also connect the Virus Snow to you computer via USB, instead of MIDI, and use the built-in USB-MIDI interface within the Snow. This is probably the better way to do it, as the USB connection from the Snow to the computer also carries audio, and can be used to route audio digitally from the Snow into the computer. as well as controlling the Snow parameters, from the Virus Control plugin.
Once you connect the MIDI keyboard and Virus Snow to the computer, via MIDI or USB, you go into MPC Software Preferences/MIDI, and make sure that the computer MIDI input that your MIDI keyboard is attached to is ticked as an active MIDI Input, and in the MIDI Mapping section, you map the computer MIDI output that the Virus Snow is connected to as one of the 4 MPC Software MIDI Out Ports (A-D).
Then within MPC Software, when you want to play the Virus Snow, you create a MIDI track, and set it to the MPC Software MIDI Out Port (A-D) that you set it as above.
