The palette case has jacks for line level inputs and outputs. You have to BUY the modules to make this functionality work. Your modular gear works at SYNTH level, which is a lot higher than line level (your Octatrack). You're also going to need a MIDI to gate/CV converter. Again, the Intellijel case has the facilities for MIDI, but you have to BUY the modules to connect to it.

So you have a Palette and two 1U modules for MIDI and audio IN/OUT and you still haven't put in anything synth or percussion related yet.

You'll probably find that buying a drum machine and plugging it into the Octatrack is probably a much better option in terms of set-up and price.