Hello Keith,
[Topic moved here.]
In order to be able to use your Orla organ to play Hauptwerk, it would need to have MIDI capability (which has been standard on most digital/electronic organs since about the mid-to-late 1980s). From a brief Internet search, my understanding is that the Orla GT9000 does have MIDI. If unsure, you should be able to check whether it has that by seeing whether it has a 5-pin socket labelled 'MIDI OUT' (or a similar name with 'MIDI' in it).
If it does have MIDI then you would should be able to use it to play Hauptwerk, at least to the extent of being able to use the Orla's keyboards, and perhaps also its expression pedal(s) and pistons to control/play their counterparts within Hauptwerk. (It may 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/#6
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.
I see I also covered previously how to configure MIDI (auto-detection, etc.) for use with your Orla in this previous topic of yours: viewtopic.php?f=4&t=16447
Searching our forum for 'Orla' finds two topics from one other Hauptwerk / Orla GT9000 user:
viewtopic.php?f=3&t=8827
viewtopic.php?f=17&t=8993