Re: upmixing... Really, it is a pretty complicated/technical discussion.. I am no expert by any means. Interested parties can research for themselves matrix/active matrix; dpl, dplii etc. ..
In the end what I did was try various programs/techniques and gave samples for people to check out & decided on the atsurround active matrix decoding.
It should be similar to official dplii decoding. Similar/different for better or worse? Your mileage may vary... But likely minute in any case..