I'd have to look at some manuals for those plugins you mention to see exactly how they function, but to elaborate a bit: the Finalizer has a normal M/S thing where you can pull down the mono information level which is the equivalent of pushing up the level of the stereo information. But using another effect available only on the 96k version, you can set up the Finalizer's Spectral Stereo effect to look at, say, only 8k and above, sense the stereo information only in that range, then it uses its magic phasing and other wizardy to push out the stereo information 8k and above. The mono information in that range is left alone. Since it gives you three bands though, the midrange band I leave alone, and I usually pull the really low stuff to mono just a bit, but not entirely.
There are definitely newer plugins that can do all of that (I'm looking at you, Ozone) but there doesn't seem to be a one-stop-shop plugin like that for OS9. If there were, I'd consider going more ITB for mastering. The Finalizer's Spectral effect, plus my mastering hardware compressor is what's keeping me from doing that.