Greetings - first post. Using R4

I insert 1 instr, which is now NN-XT 1, tehn another which is now NN-XT 2. I can hear NN-XT 1, but I can't hear NN-XT 2 at the same time. I see that it's being triggered (note on light flashes) but no sound. So using the tab button, I went to the rear and changed the connections - now I can hear NN-XT 2, but not one. So, how do I get both at the same time? I am trying to use this in Cubase with rewire, but also tried this standalone. I can kind of understand the standalone not working because my audio card only has 2 in and 2 out. But within Cubase I can't get this working either? Any help? Thank you!