Here is an example (I was using a software MIDI device outside Reaper) to get you started. -- make sure that your hardware appears as an output MIDI device and as an input audio device (or do some audio routing outside Reaper to get the hardware audio output connected to a Reaper audio input). -- add ReaInsert to track A, -- set it to Send out MIDI to the synth, -- set track A to record MIDI from your keyboard, -- set track B to Record audio from your synth. Click Record and Play your MIDI keyboard, click Stop and save the recordings. You can do this all on one track, but that is a bit more complicated: -- add ReaInsert to the track, -- set it to Send out MIDI to the synth, -- set it to Receive audio in from the synth, -- set the track to record MIDI (or Audio output (latency compensated)) from your keyboard. Click Record and Play your MIDI keyboard, click Stop and save the recording. You'll probably need to adjust some latency timings to but I have not figured out exactly what is needed. HTH