The files you are looking for are located in Swkotor/Data/sounds.bif.
If you open the utc for the npc, you will notice that there is a SoundSetFile field that contains a reference to a line in soundset.2da
Here is a document about the sounset file format:
http://nwn.bioware.com/developers/Bioware_Aurora_SSF_Format.doc)
I wrote an update to tk102's KSE (v.2.0.8) that allows you to change the soundset for your party member with a simpleclick. However, it does not allow you to create new soundset files.
I found an editor but it doesn't work with Kotor. The format seems to be slightly different. However, overwriting the .wav files shouldn't be a problem. I'll see what I can do this evening if I have enough time. (I don't have the game with me right now)