Hello caper1,
With regard to MIDI: Hauptwerk has native support for the MIDI implementations used in MIDI-capable Allen organs of which we're aware, so provided that the church's digital organ has built-in MIDI then I'd expect (although can't guarantee, since Allen might have used MIDI implementations that we aren't aware of) that you should be able to use the digital organ to control Hauptwerk, at least to the extent of being able to use the digital organ's keyboards, expression pedals, and probably most of its pistons to control/play their counterparts within Hauptwerk. (It would probably also be possible to use its stops, but you wouldn't then be able to use Hauptwerk's combination system, since the two combination systems would 'fight over' the states of the stops.)
There is an entry on compatibility with digital organs in general here:
https://www.hauptwerk.com/faq/technical/#6If you haven't already done so, please also have a quick read through the '
Playing Hauptwerk live from a digital organ' section of the main Hauptwerk user guide (pages 179-180 in the current v4.2.1 version:
https://www.hauptwerk.com/support/documentation/ ), which covers some important points to be aware of, as well as how to connect things up.
They would of course also need a suitable computer on which to run Hauptwerk, as well as suitable audio/MIDI interface(s):
https://www.hauptwerk.com/learn-more/requirements/https://www.hauptwerk.com/clientuploads/documentation/PDF/HauptwerkPrerequisites.pdfhttps://www.hauptwerk.com/clientuploads/documentation/PDF/HauptwerkBackgroundTechnicalInfoOnComputerHardware.pdfFor installation in a church, stability, reliability and maintain-ability of the hardware and system as a whole, as well as the number, power/quality and locations of speakers, are likely to be important considerations. However, I don't have first-hand experience with such installations myself, so I'll leave others to give offer their advice. There are quite a few previous threads on the forum covering people's previous church installation projects and experiences.
Best regards, Martin.
Hauptwerk software designer/developer, Milan Digital Audio.