I can't remember if I've mentioned this before, but I really wish there were a chromatic (non-key based) version of the quadravox algorithm, e.g., for multiple root-5th-octave organ sounds.
Sounds like a good idea. I think I also once wanted to play like this. Can't assure whether or when will it be updated though…
Currently, I would recommend you:
1. still use Quadravox, set the MODE to Major. As long as you don't hit major 7th notes in the key of the KEY knob, you can always get perfect 5th notes to make this organ-like sound.
2. Try H910/H949 algorithm. Set one pitch to 1.5 and another to 2.0. Turn delays to 0 (or very small) and give both voices a bit feedback (add a bit more on the 2.0 pitch voice). You should be able to get this kind of organ sound.
Hope it can help.