After reading a bit from the S6L console manual and having some experience doing this with x32's this might help. In your case it would be with Reaper not pro tools. Im not sure about the ethernet adapters though, I didnt need them for my computer.
Enable and Adjust Direct Outs
After routing a Direct Out to Pro Tools you must turn each channel’s Direct Out on and set its level.
You can do this from the external screen or from fader strips.
To enable a Direct Out and adjust its level from the external screen (see image at right):
1.Navigate the external screen to the Inputs or Outputs page, and Select (or Attention)
the desired channel.
2. Turn the channel’s Direct Out on (so IN and the encoder are lit green.
3. Rotate the on-screen encoder to set the Direct Out level.