I haven't done it with a DX7, but it's pretty straightforward to map whatever you can to external midi controllers. That solution is not as tightly coupled as

I haven't done it with a DX7, but it's pretty straightforward to map whatever you can to external midi controllers. That solution is not as tightly coupled as this solution, but it works well enough... I have a newere electribe and a midi controller with a bunch of knobs and it's a lot more fun to play when I've mapped out a bunch of CCs. So, like the "addon" is midi, but it's just a lot of work to setup maps in certain sitations, and the controllers usually don't know where things might already be set in the patch on a device. I agree that modular are much more rewarding as you really can just tweak knobs (or have the machine tweak its own knobs in stragne ways)... that's really what I prefer.