Crob,
the main differences between HEM (Homogeneous Equilibrium Model) and HNE (Homogeneous Non-Equilibrium)
with specific applications of Prode Properties software are discussed in this blog entry

'http://www.egpet.net/vb/entries/82302-Comparison-of-Homogeneous-equilibrium-%28HEM%29-VS-NON-equilibrium-%28HNE%29-models '

Hoping this helps.