https://static.kvraudio.com/i/b/surroundzone2.png
This thing?
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For upmixing 2>5.1, I would reccomend DTS Neural upmix (ORIGINAL edition, NOT the waves edition, waves has a bug with LFE). DTS Neural upmix (ORIGINAL edition) gives the most discrete channel content (if you're not upscaling dialogue, set width 100% to get 4ch out).
http://i54.tinypic.com/xq9xt5.png
NOTHING ELSE. Everything else VST ive tried nugen , soundfield , Surcode, SRS, waves um, arctan, spat, everything passive all falls short in one way or another.
I would not reccomend upmixing 2>71, but DTSnu can do so aswel.
I havce not tried iosono, blueripple/harpex, or penteo.