Yes thanks for posting the link to that video MichaJo. I read a lot of other descriptions of how to get multi channel vsti's to work in Reaper, and this is the only one that actually gives all the information to set it up.
Even still I am having problems with unacceptable latency delay for midi recording because I'm using Proteus without an ASIO sound card. Also like others have said this method of setting up and routing channels seems pretty convoluted and unnecessary to me, though I'm sure it does attest to the power and versatility of Reaper.
Anyway my work around is not to run Proteus as a VST, but rather as a stand alone app. Then I use Midi Yolk and Midi Ox (
http://www.midiox.com/) to reroute the midi signal.
Just set Proteus to use one of the Midi Yolk input channels to trigger sounds.
Then in Midi Ox > Options Midi Devices > activate your external keyboard controller (in my case the E-MU Xboard61) as a port as well as activating one of the Midi Yolk virtual ports. Then under View > port routing > drag a connection line between the input for the keyboard controller and the output for the midi yolk virtual port.
In Reaper create a track with the IO > Midi Hardware Output > set to the Midi Yolk virtual port and the track In > Midi Input > set to your keyboard controller.
Then you should be able to arm the track and record with what ever channel in Proteus you select on your keyboard and repeat for more tracks.
Oh also with this work around you can use the second set of 16 midi channels that Proteus allows, by turning on a second Midi Yolk port and setting Reaper tracks to use that as a output.