There’s a review that describes the needed work:
https://www.google.com/amp/s/www.pr...nd-technology/review-audiosourceres-demix-pro
Sounds like this is more on the spectral edit to separated stems and remix vs. one step upmix like spec.
Spec and spec web work by the pan position of sounds in the original stereo mix, giving you controls as to how to spread that mix across the surround speakers.
Later versions also look at the phase relationship of original left and right (in the spectral domain) for separation of ambient sounds, which you can route to the rears.
FYI SpecWeb 2.0 is in the works, with new features and other improvements (built in 2x or 4x oversampling being one). Should be out later this summer.
But to focus in on the re-pan question, no specweb only ingests a single stereo track. To remix, re-pan “stems” separated by spectral or other means you want a “daw” type program. Plogue Biddle, while not a traditional “daw” certainly has all the tools to remix stems.
You’ll probably need/want a mastering limiter, and/or other mastering plugins, to restore the dynamics of the original mix or at least to master your remix. Also FYI that’s one of the big improvements in specweb 2.0 is super accurate dynamics matching to the original mix (loudness and true peak or inter sample peak).