The ioStation 24c can be used in Reaper as both an audio interface and a control surface.
To set this up, first make sure the ioStation is in the "Native" mode.
To do this:
1. ) Make sure the ioStation 24c is powered off first.
2.) Press and hold the "Next" button while powering on the ioStation 24c A few buttons should be flashing.
3.) Now press the flashing "Solo" button to choose the "Native" operation mode.
This is also listed in the manual.
To setup in Reaper after choosing the "Native" operation mode:
1.) Go to the Reaper Preferences.
2.) Now select the "Control/OSC/web" category as pictured below.
3.) Now click "Add" to add a control protocol to use.
4.) You should now select the "PreSonus FaderPort FP2" protocol to use.
5.) Now choose the MIDI device ports of the ioStation 24c to use as pictured below.
You should now have a custom Reaper control using the ioStation 24c.
Please refer to Cockos for Reaper documentation and support as they have provided this custom implementation.