[wlug] A bash question

I have an icon for xmms on my desktop. I click on the icon; xmms opens in its own little window. I open a terminal. I type in it kill -9 $(pidof xmms) and press Enter. The xmms window closes. I have a bash script. A line in it runs xmms, at which point xmms's little window opens and converts a .wma file to a .wav file. The next line in the script says kill -9 $(pidof xmms), but it doesn't work to close the xmms window. That window stays open until I click on the close box in the top right of the window. Why doesn't the kill command work in the second case when it works in the first?