[karbomusic]

That's the point, those pins on the interface are the preamp, a DI isn't that, even an active DI only provides buffering - if an active DI adds gain (beyond not losing any due to passive insertion loss), then it just became a preamp. For that keyboard that doesn't need a preamp, you plug into one of those line inputs that isn't a mic/inst combo. If all you have is the combo, that doesn't magically make it a DI, it makes it having to go through the pre cuz you don't have a dedicated line in.

^That doesn't affect your tests but one is a preamp input, the other does an impedance and balancing conversion and possible buffering if active. This time is for our understanding of how they work because it is helpful to know.