I haven't done a side by side comparison but I would say DPLII with THX post-processing sounds closer to real 5.1...... Maybe the Denon 4802 is just doing a better job with DPLII than my Onkyo 696 was. However dialog sounded cleaner, the surrounds more involved and the subwoofer stronger.
If I had to choose a DPLII processor, I would definitely choose the one with THX post-processing, all other things being equal.
Regards,
geo