it looks that way - i dunno what you're supposed to do if you want to use the mike whilst gaming in 5.1 - is there not a mike input on the front?
it seems to be a trend amongst hardware designers to double up the 'ports' like that - for instance, on my netbook, the same jack socket is used for headphones and mike. you have to buy a special gizmo if you want to use both at the same time. is it really an economy thing - how much money do they really save by not giving us extra sockets?
don't worry, you shouldn't break or fry anything if you stick it into the wrong hole...
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*edit* re-reading your post, you haven't got three inputs? speaker sockets are 'outputs'. maybe i'm being pedantic, but there is an important distinction.