13.33 MIDI Output Direct to an External Synth
The MIDI output of any track selection can be sent directly to an external hardware synthesizer instead of (or as well as) to the master.
Kind: concept (user-guide-section) Chapter: 13 Working with MIDI Items Source: REAPER User Guide v7.70

The MIDI output of any track selection can be sent directly to an external hardware synthesizer instead of (or as well as) to the master. From the track’s right-click ROUTE button menu, choose MIDI output, then the device name, then the channels. Optionally, you may also disable output to the master send.