Audiofront

Confirming: if I want to connect directly to a (Roland) keyboard, I need the MIDI Expression iO? Otherwise does the MIDI Expression iO do everything that the other models do (via the USB port)?

There's no way of connecting the USB port of the original or Quattro to the USB MIDI port of a keyboard (e.g. using a USB-B to USB-B cable)?

A USB-B to USB-B cable will not work. You'll need to use an iO. And yes, it does everything the the other models do.