Hi, I just got two analog hardware synths which I would like to use as external instruments. Problem is when I open the plug in selector, external instrument is not present to choose from. I have both synths connected by usb, and audio is input in from an Allen & Heath zed 10 mixer.. I can get control with utilizing an external midi track but from what I have researched it is much better to use them as an external instrument/plug in. Do I need a midi connection/interface to get the external instrument plug in to show up? Thanks.