hallo how can i setup vienna ensemble pro in reaper? i right click and select insert virtual instrument on new track. then i choose vienna ensemble pro. then a track is created with 16 stereo sends. but i only receive audio on the first 1/2 channel.

Hello & welcome to the Reaper forum :) I'm not familiar with Vienna, but if it behaves like any other multi-out plug I've used, you'll need setup outputs in Vienna's GUI as well = route each instrument to desired output. Perhaps there???:

"route each instrument to desired output" yes i did so. but at the end i only receive audio on channel 1/2

I Don't know then, sry :( Hopefully someone with Vienne Ensemble experience chimes in.