You need to add the INPUT USB block and then route it to both the OUTPUT3 & OUTPUT4 blocks. That's it. Any track(s) in Reaper that are routed to Computer Outs 7+8 will go to the INPUT USB block on the grid. If that block doesn't exist on the grid or goes to no OUTPUT block, you will get nothing.
If you post a screenshot of your Axe-Edit preset, I can help verify if you are doing this properly. For reference, see an example of mine below.
View attachment 64341
Here is what is going on in Axe-Edit, red being the important part for you:
- IN 1 (guitar) > OUT 1 (front of house) & OUT 4 (in ear monitors)
- IN 2 (bass) > OUT 4 (in ear monitors)
- IN 3 (drum mix) > OUT 4 (in ear monitors)
- IN 4 (vocals) > OUT 3 (front of house, no longer used) & OUT 4 (in ear monitors)
- IN USB [COMPUTER OUTPUTS 7+8] (back tracks + click tracks) > OUT 4 (in ear monitors)
- [hardwired from COMPUTER OUTPUTS 3+4] (back tracks) > OUT 2 (front of house)