I also have a four-channel-setup, and in a stereo-set I always assign a complete division to a channel.
With Hereford I did as follows:
Great to Front
Choir to Rear
Swell to Front
Solo to Rear
Pedal to Front
If you want a similar sound to the real organ, you should assign all divisions except the Choir to Front. I tried that, but found it not practicable.