I have ordered a usb to midi interface cable from musicians friend and a midi thru box. I am going to connect the usb to midi out connector to the midi thru box then run two midi cable from the midi thru to the SD-20 which only has a nmidi in connection, and one to TC helicone voice tone harmony 'M' midi in port. I will not use the usb hook up to the SD-20 just the MIDI in connection on the back of it. Widgets from musicians friend will be here late next week then I will give it a go and let you know how it worked out.

Emailed TC helicon about the thru box and they say it will work