I was always very unsatisfied when adding reverberation to Hauptwerk sample sets. I had implemented reverb via Reaper following the tutorial on the Hauptwerk website. However, I was very disappointed, as audio was always very distorted and did not sound natural.
After lots of experimentation, I found a way, which makes a whole difference. The implementation is very simple: reverberation is routed through a separate channel, which receives output from all Hauptwerk channels. This allows changing the volume of the input and reverberation channels independently. This YouTube video describes the required steps to install a reverb track.
I reduce the volume of the reverb track approximately 10 to 20 dB. This conserves the crystal clear dry or semi-dry sound but adds nice reverberation without distortion. This setup really makes a huge difference! Give it a try!