We have recently been told by a couple people now that the HX series can host midi usb. We haven’t tried it yet ourselves but it would be cheap for you to attempt, you would need a usb mini B cable for the c4 and whatever usb connector the helix has (I believe it’s a full sized B connection but not positive). From there your helix will at least be able to send midi pc messages to change presets, but I’m not familiar with helix so I can’t tell you whether or not it will send midi thru data over the usb connection to allow the morning star to communicate with the c4. If you go from the morning star, you will need some sort of usb host adapter (disaster area micro ghost works, the Kenton usb midi host looks like it would work too, but we have not tested it to be sure). The morning star, to my knowledge, is not capable of hosting usb midi devices, so it won’t work to connect it straight to the c4 from its usb jack.