Multi-Out will enable you to route each part of your drum set (kick, snare, toms, etc...) to different channels within Reaper. After executing this function you will be to process your drum tracks with your plugin library.
The following information will provide a step-by-step walk-through:
Please start by inserting a Virtual Instrument on a new track and selecting the SSDSampler.
The following window will appear:
Click yes. This will create a series of tracks in your mixer.
Within the SSD Sampler you can route your channels to each of these tracks.
This is done by clicking on the bottom of the mixer. I have routed all Kicks to out 9 mn, Snares to out 10 mn, Toms to out 2 st, Cymbals to out 3 st, Ovhds to out 4 st, and Room to out 5 st.
AU output 17 = out 9 mn
AU output 18 = out 10 mn
AU output 3 = out 2 st
AU output 5 = out 3 st
Feel free to route your tracks differently as this is what works best for my needs.
Download Reaper Session
Please feel free to download the following Reaper session that already has each of the tracks routed and labelled for you: http://download.stevenslatedrums.com/ssd4/sessions/SSD4%20Reaper%20Multi-Out.RPP.zip