The question is asked, what are the secrets to superior sound? I'll throw my 2-1/2 cents worth in.
First off, as quite a number here have already pointed out, it has to do I feel ultimately with the room and the use of the room. At the top of the list, speaker quality, response and placement is probably number one, the number of speakers and how the sound is divvied up between them is right up there as most important as well. Superior sound to me has always been about strategically using the room as best as possible within it's given variables and limitations. Some rooms are going to give better results, some poorer or will be more of a challenge. Second comes the sample set itself and its quality. As we know, there are many sample sets now available, some are going to be better in a given acoustic than the next, and we all have our preferences as to what sounds best to us.
A few 'mainstream' electronic organ companies have been mentioned here. My most recent experiences have been with the Walker that's been installed in our church for a number of years and a rather pricey Rogers installation at a church my brother and family attend that was just built a few years ago. As for the Walker, they definitely gave considerable thought to speaker placement. I've had a good chance to look things over, last I counted there were 31 speakers of the same size, the majority of them laying on their backs pointing upwards along with a large 15" sub and cabinet, I assume given the number of amps they are using some sort of cyclic or dedicated arrangement as to what stops get sent to which speakers. Seating capacity at the church is around 1400, when the church is empty it sounds fantastic, when the church is full, not so as the sound gets very dulled or muted as it fills the space very nicely empty but gets cut down to sounding like they threw the organ in a closet when the church is full.
As for the newer Rogers.... Here they really screwed up. They started out with a given speaker placement behind a wall up in front near the altar and also implemented the use of the PA speakers positioned from the front to the back of the church, even out in the entry area as well, creating kind of a surround sound if you will, the sound was fantastic. I remember walking in the first time and thinking, wow, this really sounds good. Some of the folks complained about the PA system and not being able to clearly hear the readers, etc., so they went in and re-did the sound system, moved and changed the speakers, and eliminated the idea of including the organ in the PA part, now only using just the speakers behind the wall up front. This cut the sound quality in my opinion in half, and once again when the church is full the sound gets knocked down considerably.
One challenge I've faced is creating the 'head room' you hear in a large church / cathedral acoustic, this is very difficult to create in our small Hauptwerk spaces at home and no piece of equipment, or sound modifier I've encountered comes close to doing the job. I think 'head space' in the sound is where it's at.
I think it all boils down to the room, its shape and the overall size, the bigger and more reflective the better as I can say when visiting the local Cathedral or Basilica here, regardless of how full or empty these places are the sound is still outstanding. I think this is mainly due to the fact we're looking at ceilings that are dome shaped and are way over 100' high. Much of the sound is being reflected off the hard surfaces above the organ and the sound is coming down mainly from up above, at the Cathedral here the sound literally pours down on you from above. But, place these instruments in the smaller places I mention above and I'd bet we'd still see the same results even though they are real pipe organs.
Marc