It's a bit complicated, but possible. I didn't worked with them for a long time, here's what I remember (note: everything about file paths or formats will work for NON-Steam version; I don't know if it will work with Aspyr patch)
1) Prepare your sound files (IIRC, 16 bit mono uncompressed WAVE), put them to X:\your_path_to_the_game\SWKotOR2\StreamSounds.
2) Now you need to add new line for EACH new sound to dialog.tlk. In the text field you may type anything, it won't be seen in-game. In the Sound Resref field type filename of your sound without extension (so, if file called "soud1.wav" type "sound1"). Remember row numbers for your new lines.
3) Open KotOR_tool SSF editor, click File->New. You will see the list of events for which sounds should play (like "Battlecry 1" or "Pain Grunt 1"). Next to the name of event you will see an editable field with "-1" in it. Here you need to type row number of your new line from dialog.tlk. If you have done everything right, you'll see name of your sound file and whatever you typed in "text" field of dialog.tlk in next two fields. Fill everything you need (if you don't want to use some events, leave them with "-1"), and save your new *.ssf file.
4) Final step. Open soundset.2da, add new row. In the "label" field type the name of your new soundset (like "MyOwnSoundset"), in "resref" - name of you *.ssf file without extension, in "gender" filed type 0 for male soundset and 1 for female one. In "strref" and "type" fields write ****. Save your changes.
5) Congratulations! Now you should be able to set you new soundset for characters.
Sorry for my English, I hope I explained everything clear.