I have a polygonal object which contains several polygon groups (i.e. it isn't a single mesh) I can use a Connectivity SOP + Partition SOP to create the polygon groups. But I need to emit one particle from the center of “it's own” group and then attach that group to that particle. Any ideas how to do it?

One way would be to use an add sop to delete geometry but keep points and then build new polygons using the ‘By Group’ option. Use those messy prims to generate your particles. With primitive sop you can move those polygons with your particles. The point numbers don't change so put down a point sop and copy the chaniging positions from the moving parts to your initial model. See the attachment.. hopefully it'll make more sense

This is it! Thanks