STAM, yes Kontakt can be used as a standalone synth. You can play midi or style files if you preload all the appropriate instruments in the 16 channels. Kontakt does not do a very good job of accepting program change numbers. This apparently will be fixed over the next few months. In any event, you can just load an instrument, switch your keyboard to the appropriate channel (plus turnoff local) and play.
Kontakt has very good effects. They are so good that todays computers are not powerful enough to handle the convolution reverbs. You need to balance quality with your computer and your needs.
As I pointed out in other discussions, Kontakt has a few bugs. It may be worthwhile to wait towards the end of the year to spend your hard earned money. If money is not an issue than go ahead and acquire it. It is a very good synth/sample player-top of the line. This will give you a chance of getting acquainted with it and when the fixes come (Kontakt v2.1) you will be ready to make beautiful music.
Kontakt is a very complex piece of software and probably is upgraded every 18 to 24 months. In addition, the virtual acoustic samples for pianos, organs, saxs and so on are also continually updated. So while the sounds are the best you can get.....it is very expensive.....if you go top of the line. You can start with Kontakt and the Kontakt Library but even as you noted this to is expensive.
There are are other lower cost solutions to test whether you would like to go this approach, e.g., soundfont synths and instruments. These would not necessarily be better than your Korg Keyboard.
Furthermore, I agree with AJ's comments.
[This message has been edited by Frank L. Rosenthal (edited 05-14-2005).]