I've been playing church pipe organs for over fifty years, and also have Hauptwerk. The best discussion I know of regarding speakers, and digital versus pipe organs, is at
http://www.pykett.org.uk/EndOfPipeOrgan.htm
Basically the message there is - the more speakers the better, in order to minimise distortion, especially intermodulation distortion. My Hauptwerk installation uses twenty speakers; if I had the space and could afford more, I would. The main speakers are two groups of eight (four stereo channels), using the algorithm “cyclic with octave, octaves and ranks cycled”.
The late Leo Christopherson used around eighty speakers, and his recordings on contrebombarde are the most natural I've heard. Search on “CHRIS_037”. This example shows how his system sounds with various stop combinations:
http://www.contrebombarde.com/concertha ... music/3335
You don't say where you live, but in the UK there is such a shortage of organists that anyone who shows an interest in the instrument is immediately made very welcome. If you ask around you might well be given access to a pipe organ, especially if you offer to contribute to the cost of electricity!