Multiple audio sources problem

Hello everyone,

I'm currently a streamer for a famous sc2 french team, and i needed to improove my audio settings during my stream, so i wanted to add a second mic to my shoutcasts. To acheave that I followed many tutorial about the procedure to mix multiple audio sources in to one virtual audio line, using VAC and audio repeater.

I succeed to do this, but now I have an other problem :

http://image.noelshack.com/fichiers/2013/28/1373818559-capture.jpg

As you can see, my system sound is using "line 1" as default peripheral device, so that i can not hear the system sound in to my speakers, and the system sound is now on the mic line, and this will be a problem for the recording of this line as a mic line, and not a sound line.
My question is, how to change default peripheral devices for any applications, as system sound is, or other applications like teamspeak etc...

for example, i need the system sound on my speakers, and not in line 1, how do I do that ?

thanks for your time, I hope you guys can help me about that.
sorry for my quite bad english expretion by the way,
sinceraly,
 Arthur TOUZARD