you did not read what i said. please read it this time carefully:
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your first problem is getting analog output from consoles given that you want to use analog 5.1 headphones with them. regardless of any kind of switching, you need to solve this problem first.
now, you could run two such boxes but for $35-50 cost that would be a bit costly which is why i suggested getting one box and hooking it up to both consoles with a switch. if you want to get technical, you could use a 3-way hdmi switch and hook it up to all 3 devices however i did not list this because it would bypass your good soundcard which you do not want to do. this is why i said to run a simple hdmi switch (2way) for the consoles only
okay, now you have two (assuming you're using a hdmi switch) sources of 5.1 audio. since many hdmi extractors have rca jacks not 3.5mm you'll need 3 adapter cables. once that is done, you should have two sets of 3 3.5mm cables. that is where the switch i told you comes in - you can DIY your own switch to do what you want. i'm not aware of any 5.1 two way 3.5mm switch. i'm not saying one does not exist (you can look) but that i have not seen one before.
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if you were using 2.0 stereo headphones its a bit simpler. while you could certainly use hdmi audio extractors to pull audio you can get away with much cheaper usb soundcards (google usb to 3.5mm console) and buy one for each console. now, you will have 3 sources of 3.5mm stereo audio. you can find 3.5mm stereo to 3 or 4 way switches easily (may be called 4 port speaker selector)