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http://www.audiomulch.com/
PC routing.
You have to use reaper as a master. In audiomulch you set the audiodriver to asio rearoute and change SX3 to rearoute asio driver and vstconnections for your rearoute master output.
This is for playing vsti through SX3 and reaper routed to a reaninjammtrack with your asio soundcard latency ;-) (You have to disabel your midi input in Reaper to actually play the vsti in cubase)
All the other routings you prob figured out.
PS. Any output over the masteroutput in SX3 are also routed to reaper