Unless itunes has the option in it somewhere to use other than the Windows default device, no. If it does set the headphones as the default device, and in itunes set the speakers as the playback device.
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If you mean 3.5mm plugs to sockets then i think you'll find the OP can't/won't benifit from them has i believe from the picture he posted his headset is USB due to the fact it is showing up in the sound options menu. A standard 3.5mm jack hesdset wouldn't show up in there. I know because i also run 5.1 speaker's + 5.1 headset off 3x 3.5mm splitters.
The only real option is through software as Stormy suggested. If not through itunes then maybe through his soundcard's software.
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Asus Xonar D2
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i did not see that it was usb. You get a spliter run the one line to the out door speakers and the other into the mic port on the motherboard and then have the headphone speakers listen to the mic port (under the recording tab) on the motherboard. This will still all you to hear music inside and outside.
You may also be able to get it to work without the spliter by getting creative with the recording tab settings.
My Computer
At a glance
Windows 7 Pro x64 SP1 and Mac OS X 10.8.3Intel Core i7-3820 Sandy Bridge-E at 4.75 GHz8 x Corsair 8GB DDR3 64 GB Kit @1866 Overcloc...GTX 580 and MSI R6870
1 x Corsair Force Series GT CSSD-F60GBGT-BK (OS)
2 x Western Digital Caviar Black Sata III 750GB (Raid 0)
1 x Western Digital Caviar Black Sata III 1TB (Media)
2 x Western Digital Caviar Black Sata II 640GB (Raid 0)
4 x GELID Solutions FN-TX12-15 120mm Case Fan with Superior Temperature Control
1 x Corsair 140mm Case Fan
1 x SilverStone FP55B Aluminum front panel 5.25" to a 3.5" bay converter
1 x Ultra Card Reader
1 x Sony Blu-ray Burner BD-5300S-0B