Most of the attempts to do digital pipe organs that are roughly equal to their purely analog cousins end up using substantial chunks of the physical infrastruct

Most of the attempts to do digital pipe organs that are roughly equal to their purely analog cousins end up using substantial chunks of the physical infrastructure of the analog versions - the building, and sometimes even the pipes themselves, generally per-pipe transducers ("speakers"). You can reproduce the 3D soundfield of a big organ using wavefield synthesis. I heard a phenomenal recording/reproduction of a performance of a Messaien piece recorded in the Koeln cathedral and played back at the TU Berlin with their 4k+ speaker wavefield synthesis system. You can walk around in the room and experience the actual "space" of the cathedral.