Separate the flowers from the cauliflower head. Chop all of the other vegetables, including the remainder of the cauliflower, into bite sized chunks. Put the vegetables, rice and broth in a large soup pot and simmer for 45 minutes (rice and vegetables should be tender).
Puree everything in a blender or food processor adding the soy milk. Adding the soy sauce is optional. Simmer for 10 to 15 more minutes, and serve hot.
I've made this with asparagus or potatoes instead of cauliflower. It also makes a good sauce for over vegetables and/or grains.