If you're only using the keyboard at the moment, you should be able to connect the keyboard MIDI Out to the Carbon Sequencer In, and the Carbon Sequencer Out to the keyboard MIDI In.
That would enable you to record your performance to the sequencer, and play it back - and in both instances you should hear audio (just double check how the MIDI monitoring is set up in the Carbon, and that the keyboard is receiving that data on the correct channel).
From there, you can insert the DoReMIDI at the output of the sequencer, and connect all remaining devices (including the keyboard).
If you look back at that video you posted, that guy was programming his drums on the Arturia Drum Brute, and using the Carbon Sequencer to trigger those patterns (the kick, snare etc sequence was not in Carbon, it was in the Drum Brute).
That's how you would use the Roland 303.
Or alternatively, you would use your master keyboard as a controller, and perform / program the sequence in to Carbon.
Similarly, the Moog (I'm assuming you meant it only has MIDI In).
You're basically using them as sound modules, controlled by the keyboard, and by Carbon Sequencer.
MIDI over USB works great, but if you wanted to take advantage of that you're either incorporating a computer, or purchasing a 5 pin din MIDI to USB converter, or doing both.
