If your on windows and just want to pass audio and midi back and forth minus the clock / timeline sync Id say forget Rewire and just use ReaRoute for the audio and loopMIDI as a loopback MIDI-port.
I do this all the time and once its all set up it works great.
That being said I only send from Renoise to Reaper not the other way around but I assume It would work exactly the same.