I have a Focusrite 18i20, and haven't been successful so far trying routing inside that.
Granted attempts are being done at night with limited time (due to work), so I wouldn't doubt the routing can be done, I was just seeing if anyone else had some tips.

As for 'inside RB', *usually* I can use the Input Monitor feature and (for instance) play guitar thru a VST and record it live, but that is pretty much all Audio.
It seems to be the MIDI side that is giving me issues.

I am using the keyboard USB direct to computer as the trigger/driver for MIDI.
Maybe I should try routing MIDI through the 18i20 and see if it behaves any differently.
.. or maybe this is why Matt switched to Presonus; because the difficulty of doing such things with an 18i20 is complicated, if possible

Or maybe I need to use Kontakt as a standalone, and route stuff inside of there. I haven't got that far yet as I am still getting used to Kontakt, which in itself can be a bit complicated

I do not work here, but the benefits are still awesome
Make your sound your own!