What the csm seems to do is filter the up and downstream data, (for want of a better way to put it lol), What I have noticed is that all the above example's of how to code these commands into a button dont work, I have tried quite a few combinations of my own also...
Somthing to note is when you type in /csm play , it comes up as an unrecognised command and rightly so as it is as far as SoE is concerned, but despite this it does start playback with csm's mp3 player anyway after a short pause...
I think I said this elsewhere..
The only way I can see this working from a button was if there is a way to input the command into the chat window and include a <cr> as if the user had actualy keyed the command in..... As you can get this to work using macros I do know that much..
EDIT
Also thanks Aden for including this mp3 player in your csm, Nice one