Win7 hdmi audio & pro logic?

I've been trying to get hdmi audio working properly for my htpc. The audio is coming out of an ati radeon hd 5770 and goes through my Sony STRDG720 receiver and then on to my TV. I have the audio set to 7.1 in Windows and I can only seem to get audio out of the two front channels for stereo sources. I understand that windows is padding everything except the two front channels when multichannel audio is not being played. So I just want to be able to use pro logic IIx on my receiver to fill the empty channels. However whenever I try switching surround modes my receiver displays "NOT USED". I have tried changing the speaker setup in windows to output only 2.1 channels and this setting is reflected on the receiver display, but it still does not let me change the surround mode on my receiver. I am able to do this with ps3 using hdmi audio so I would assume this should work.. So I'm not sure what the problem is. Any help would be appreciated.
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More about win7 hdmi audio logic
  1. Within Windows, whether you set 2.1 or 7.1 shouldn't matter. If the source is 2.1, it will output as 2.1. You should then be able to apply Pro Logic via your receiver without a problem.

    Check your manual, as some receivers are picky when it comes to HDMI audio. May need to use a specific input port or something of that nature.
  2. Alright thanks for the help. I just figured out what the issue was though. I had the PCM frequency set too high on Windows. Apparently my receiver can pass through up to 192khz 24bit, but it can only decode pro logic up to 24bit 48khz.
  3. ^^ Makes sense; all Dolby formats are 48KHz output. A bit surprised the receiver wasn't smart enough to simply allow a downmix to 48KHz then do Pro Logic though...
  4. Yeah, I still need to set it to 2 channel audio for it to allow me to change surround sound modes though to pro logic and the like. When it's set to 7.1 on Windows it still displays "not used" on the receiver when I press the A.F.D. button. This is just a minor inconvenience now though, as most of what I listen to on my computer is not multichannel anyway. So I guess if I want to listen to true 5.1 or 7.1 I just need to change my speaker mode in sound settings on my pc.
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