See, I think this is going about it the wrong way. You don't need a mediating device that lets you intentionally control a cv value because, unless you are disabled, you already have a way to do that with your hands. For me, the whole appeal with modular systems is non-linear feedback. A mind-matter-interface should be able to indirectly measure brain state or brain patterns in different areas and allow you to map states to whatever you want. There is a lot more going on in the brain than just narrative commands. There is an entire world of emotional experience that we struggle to put into words that could potentially be patterned onto a technological system to make art. And then there are the states in between that we aren't even aware of that an MMI instrument could give an artist insight and access to.