So the laptop with an HDMI cable connected to the projector for the picture. Picture runs.
All that remained was the sound. So buy this Asus Xonar U3 USB external sound card and software installed (under Win7 - 64bit). Plus bought a short USB extension cable.
The sound card is now suspended between the optical light guide cable and the USB extension cable so that it feels like you could have just one cable that you just plug into the PC. Thus, the sound card is hardly noticeable. Excellent!
And what gives me great pleasure: I put the USB cable into the laptop, the PC automatically switches to the external sound card with digital Dolby Surround 5.1 and the digital receiver will switch to using.
I pull the USB cable out again, the laptop speakers to turn on and the sound running back over the built-in on-board sound card. Did not think that works so well.
From the Asus software that I, by design, rather BonBon-ig find (there are videos of it on the internet), I get to do anything because I do not have to actively use - runs so in my case, everything in the background.
The sound is impeccable.
The two blue LEDs would be Asus can save, but they do not bother me further.
The price is totally OK.
From me there is an absolute buy recommendation!
