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I'm pretty sure that if you have something plugged into the line-out on the back of the machine (e.g. speakers) and then you plug in a set of headphones into the front phones jack, the headphones would override whatever is plugged into the back. So, the answer would be no.

But you can also go to just about any electronics store and buy a 3.5mm stereo Y splitter (shouldn't cost more than $5) to split the line-out in two.

If you don't mind buying online, they're SUPER cheap at Monoprice:

http://www.monoprice.com/products/p...d=10218&cs_id=1021802&p_id=667&seq=1&format=2


EDIT: Whoops, it seems that Monoprice is backordered on these. PartsExpress has these, too:

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=240-130
 
Get a Y splitter for your lineout. No, the Headphones jack on the front doesn't override the line-out. Google and download "SoundMenu". Its a great little app that runs in the menubar and allows you to quickly switch inputs and outputs, instead of having to go into system prefs.
 
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