I'm glad it was helpful.
The mixer is a JS plugin, and I'm pretty sure it comes bundled with Reaper. Search for ix/mixer. There are 2 versions,
- an 8 mono ins to 1 stereo out where each mono channel has volume & pan control,
- an 8 stereo ins to 1 stereo out that has volume only for each channel.
Heads up: you only "see" this mixer when you open the FX window for the track.
As far as routing the outs to different tracks: Kenny Gioia has some great tutorials. Here is one:
https://www.reaper.fm/videos.php#uFuR7K1HSNw
for creating a drumset with multiple outs from a master MIDI channel routed to separate channels.
I don't have the Garritan Personal Orchestra, but from DarkStarS post, it looks like you can setup the routing to separate channels from the plugin itself.
Kenny Gioia's vids are great! you may want to check them out anyway. There are tons of them here:
https://www.reaper.fm/videos.php