"that you want to play 2 instruments at once , with , lets say , 2 keyboards "

No. One keyboard.

Let's forget about Cubase for a minute, because i can not get this working in standalone either. Let's forget about keybaords as well. I have two instruments loaded, two NN-XTs. Two tracks with MIDI data. Track one triggers NN-XT 1 - I can hear that. Track two triggers NN-XT 2 - I can NOT hear that. Question is why? Well, I see why - NN-XT 2 is not routed anywhere. I can not route BOTH NN-XTs to the outupt at the same time. If you can't route both to the main output, how are you supposed to hear both?

Thanks again.