You can try a variety of searches on Google: 'po hun soul', 'Chinese mythology soul', 'binary soul' turn up some interesting things. Unfortunately, this idea has been heavily usurped by New Agers, Pseudo-Medics, and Gamers, so many sites may deal with this concept from these aspects.
I originally heard of this concept from a gaming book, in fact: 'Mystic China' by Palladium Books. But I then read a long book about Chineses Mythology, one geared more toward the common, everyday beliefs of the people rather than the formal mythologies of temples and history, and it discussed the Hun/Po model in more detail.
In some concepts, the Po is permanently tied to the body, and descends into the Earth upon the body's death - this is the source of some Chinese myths about the undead, that the Po can reanimate the body. The Hun ascends into the spiritual realm and becomes either a Heavenly spirit, or it fails to do so and remains on Earth as a ghost. This is partly why the Chinese seek both physical and spiritual harmony, and why they respect the burial places of their dead so much: they think some connection between hun and po remains, and a disturbed body might invite the Hun to return to redress a grievance.