I would like to know which ones of the following DAW (for pc) software allows editing and saving (non-destructive) 24 bit/192 kHz audio files in their current or soon to be released versions…
Cakewalk Sonar
ProSonus Studio One
Pro Tools
Steinburg Cubase
He he, as i actually am a professional sound engineer (well at least in my “real” life) i can tell you, that it is not easy to tell … because … errrr … they all do 
Most of them actually do 64-bits floating point.
Concerning your specs. As long as we are talking about simple mastering you should be more than ok. But as soon as you start to use a lot of FX in your mix, or do extensive multitracking, that is the point when your comp will start to slow down causing timing issues.
Thanks dsoellbuster
Please post some insights to sepecs
… in addition to what dsoellbuster pointed out (and to answer the soundcard part of your question) >> yep, a capable audio interface would certainly not hurt to have around.
These things come in flavors, and you can get them from most of the internet music stores.
In my case (owning a lesser machine then yours) I found the interfaces made by Line6 the best for my needs (like “guitar port” or “PODxtLive”). Although most of them are “themed” for guitar, there are a few that contain keyboard (physically) and microphone gear as well.
Working with Ableton live, well - multitracking, fx-ing both audio and midi without bringing my old machine down.
My son (sound engeneer, too) uses pretty much the same tools (added a MACKIE-control, VERY useful!) on his MAC’s for home work (the fun part of the job 
).