Are you referring to unmaking audio? I use Steinberg's SpectrraLayers Pro as I am a Cubase user and whatever the last installation of it becomes resident as an extension but it does run standalone. I use it for things like audio repair and manipulation.

I think the other 'big name' in the field would be the RX10

None of them are perfect and it can be quite tricky to isolate to a forensic depth but I also know that SpectraLayers has better tool customisation and thresholds and also better layer management.

I suppose, like most audio things, people will tell you that the one they use os best so I wouldn't;t just take my word for it.

demucs is pretty good. It can be run locally, for free. I haven't tested it with 5.1 channel audio, but by default it splits the stems into bass, drums, vocals and other.