1. Set up
loopMIDI and start it. Click the add button if there isn't a connection already in the window.
2. Start Reaper, add a track, and set the source to ReaRoute 1. Click the button to turn on monitoring unless you want to feel like a fool later the way I did.
3. Add a Virtual Instrument track with MIDI transpose as the instrument. Go to routing and set it to loopMIDI.
4. Set both of those tracks to record mode.
5. Start VCV.
6. Set VCV's MIDI input to loopMIDI.
7. Set VCV's audio output to ASIO/ReaRouteASIO.
8. Patch your audio to output one in the VCV window, and you ought to hear it piped back into Reaper.
To send audio out to Rack for processing, just choose ReaRoute as an audio hardware output, and select the matching channel in Rack's audio interface module.