I've defined two of my two audio interface through the Asio4All driver but I cant see an option for two inputs in Reaper, how can I use all the four inputs of my two audio interface (2 in each everyone)?
1) Under Preferences > Audio > Device: make sure that ASIO4ALL is selected as Driver and that the Input range is set correctly, as Stella645 mentioned above.
2) Then choose an appropriate audio input for each Track:
Multiple Audio Interface
Linear Mode
