If all you are looking to do is replace some of the GSYE files (gsye01.ogg - gsye12.ogg) and as it seems you've already unpacked the sound.dat file, all you really need to do is determine which gsye**.ogg file(s) you want to replace.
You can usually listen to .ogg files using Windows Media Player ~ you may need to right-click the .ogg file, select Open with> Choose default program...> Browse... and navigate to the C:\Program Files\Windows Media Player\wmplayer.exe and after double-clicking the .exe be sure to tick the 'Always use the selected program to open this kind of file' and press OK ~ You may/may not get an error from Media Player along the lines of 'The selected file has an extension (.ogg) that isn't recognized...' Just tick 'Don't ask me again..' and 'Yes'.
Once you've determined which GSYE file(s) you want to replace you need to have files to replace them. As long as you do, you can simply rename your replacement files with the same number designation of the ones you want to replace and put it/them in the 'sound' folder. These will then overwrite the gsye**.ogg files in the .dat file. You can also, if you are so inclined, delete the 'unpack' folder as you no longer need it.
I hope I explained the process simply enough?