- say, for the sake of argument, that the OP wants to do what you mentioned, BUT it's only when asked for more info that you learn their Graphics card has a unused DVI interface, and they were using the factory stereo internal speakers on the TV, not realizing that they could simply pull the HD vid thru a DVI-to-HDMI cord and enjoy the same stereo sound from a rear 1/8" phono stereo jack out and a similar male-to-male 1/8" (3.5mm) phono cord, assuming there is a 1/8" phono audio in option on the HDTV as most have. most audio cards will allow the front jacks to be bussed separately, from the rears by a mere checkbox, and you would only need one device (i guess its technically 2 but it allows it, front=headphones device, rear=speakers device). Tweak a few sliders pots in the appropriate device audio tabs so the sound is routed correctly and job done. Even easier if the purpose was to play the same sound through both the speakers and the headphones, because say...i dunno someone is has a hard time hearing the TV, or likes to use a headphone unit with a built in volume control potentiometer, because the TV's too loud for them usually! same setup , just not onscreen slider tweaking! easy-peasy. right?!
I'm sure I'll be wrong but, hey, I heard "impossible" a few posts up and became intrigued enough to ask "why" at least!