There are 4 parts that work together to make this happen:
- MIDI keyboards and pedalboard
- Audio/MIDI converter
- Computer with Hauptwerk installed
- Audio system - amplifier and speakers
The system can be as elaborate as having a traditional console with moving drawstops or it can be in a minimalist console with touchscreens instead of drawknobs.
The advantage to using touchscreens is that it allows you to instantly change to load play a different organ without having to adjust your console.
You can go from using a 1721 Silbermann organ which is 3 miles from Bach's house to playing a Mutin/Cavaille-Coll organ that Widor himself inaugurated. These organs would ordinarily be laid out very differently, but the screens allow everything to change seamlessly.