When I was in Freidburg, Germany a few weeks ago, I visited the large cathedral there. It is home to 4 magnificent pipe organs placed strategically around the building.
Our tour guide stated that there are a total of 10,200 pipes & that each organ has its own keyboard plus a master station that can play all 4 simultaneously. It takes a special organist to successfully accomplish this due the length of time that the sound takes to reach the master station along with the 6 second decay time in the building.
There is a CD & an SACD available showcasing all 4 organs playing simultaneously by EP Biggs that I would like to get but, since it so rare, it is prohibitively expensive. Info here (first review on the page):