360 + mixer?

Heya guys. i have a very strange question that i doubt any one will be able to solve but just incase...i bought a 8 track mixer for school, and it is both midi controled and of course, anolog. i have my 360 on chanles 4 and 5 so that i can have the sound going threw my computer speakers but... i have NO volume going to the subwoofer. even tho when i plug my mp3 player into the same 2 channles i get sub volume. WHATS UP?ive also tried using the first 2 channles and using the mixer manual, it should work! it is set up right and every thing. and before i get asked why i even have a mixer, ill just tell you im training to be an audio tec and it makes using the software mixers a lot more natural... but it has oter uses such as this. 360 + mixer?
oh and im using the componint cables ( spelling) audio. i tried with rca and i get the same results..360 + mixer?
no one?

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