This is a long question. I use the 990 connected directly to my HTPC. The HTPC does it all--plays DVDs, plays digital and analog TV, plays games, plays music. So all output is via the onboard ALC882D Realtek HD audio chipset on my motherboard, connected with a Toslink to OPT1 on my 990. If I am watching TV, on my 990 screen, the following are lit up(shown in the order they are on the Display:
Dolby Auto
PCM ProLogicII
Digital

With a DVD, I see only Dolby Digital ProLogic

I switch the music to upsample or bypass and it works fine.

What got me wondering about audio was trying to output 5.1 from the game Battlefield 2. They have a hardware option which I checked, and I was missing the center(which I don't have--990 set to "none") audio, and the rears. I then went to the Realtek software to see what I could change. On digital, it simply offers sampling rates(44, 48, 96, 196(?)) and whether SPDIF out is enabled or not. If I use their own test where the bee flies around the room, it is only present left and right front, no rears, and no center zone, despite setting it for 5.1. So why is the chipset not outputting a straight digital signal to the 990? Should it not just send data to the 990, which will do any necessary decoding?
What about the PCM I see on the display--what does that indicate about the output of my HTPC?

I guess I am confused about exactly what is coming out of my HTPC, and whether I should be getting something different/more/??? I do not see any place where I can get a SPDIF passthrough, which I think would be best.

Any help appreciated!

When you are watching TV, you are feeding the 990 a PCM signal (which is why "PCM" is lit up) via a digital connection (which is why "Digital" is lit up) and the 990 is applying Pro Logic II decoding (which is why "Dolby" and "Pro Logic II" are lit up). When watching a DVD, you are feeding it a Dolby Digital bitstream over that same digital connection, so PCM cuts off. It's hard to say what the DD bitstream is (2.0 or 5.1), as it should vary from disc to disc.

How many speakers do you have set up? You mention the absence of a center (which can be dealt with at the 990 - the HTPC doesn't need to know that).

I have 2 front, 2 rear, and a subwoofer, and set up the 990 with center set to "none".

How about OTA HD? If the local broadcaster sends DD5.1 through the broadcast, the 990 will switch over automatically?

The Realtek test is what really gets me. Is it applying its own decoding before the signal goes out to the 990? If so, I'll be darned if I can find where to set it to "passthrough".

I found this on another forum when a guy asked a similar question:

"That is normal, S/PDIF is a 2-channel interface. The only way to send more channels then 2 is to use a compressed stream like Dolby Digital or DTS. That 3D Audio Demo is a test using PC 3D audio algorithims and not something consumer audio devices understand. "

Perhaps, then, the only issue is with Battlefield 2's handling of 5.1 sound???

The 990 will automatically detect whatever input signal it gets - no need to worry about knowing what the signal format is and manually selecting that at the 990.

I'll tell you a little trick: there are two sub indicators on the 990's little graphical speaker display (left side of the front panel). One is for LFE. If the 990 is getting a 5.1 signal, that will light up. If it is a 2.0 signal, the LFE light will be off. I have gotten to the point where I can tell with a glance if I'm getting 5.1 from a DVD or HD broadcast thanks to this. If you have the latest firmware installed, you can also press one of the surround mode buttons on the 990's remote (Dolby, DTS, or Stereo) and the front panel will scroll the surround processing mode currently being applied. That's less immediately informative as to the incoming signal type, as there are probably half a dozen or more possible surround modes that can work with any given input type.

I may be unfamiliar with some HTPC terms, but if we split hairs SPDIF is technically not a two-channel interface. SPDIF is a digital connection type that can carry PCM stereo bitstreams, Dolby Digital bitstreams, or DTS bitstreams. It was developed for PCM stereo from CD's, of course (back in the 80's, we didn't have DD or DTS), but the Sony/Philips Digital InterFace works with any one of those three. Keep an eye on that "LFE" indicator on your front panel to see if the HTPC's giving you 5.1 or not - should help trouble-shoot what it's doing.

Thanks Gonk--that was another thing I was going to ask about, the LFE light.Thanks for the tip.

There's really a lot of information tucked away in the 990's display - even though there are a few things I'd like to have laid out differently, it's hard to fault Etronics for being thorough. The speaker indicators tell you both which speakers are configured (you only see the left/right front left/right surround, and sub icons while I see the center and rear surround icons as well), while the speaker labels tell you which channels are presently in use. The separate "SUB" and "LFE" indicators also tell you whether or not the input includes a ".1" channel, which (as we've already talked about) can be handy. The field of little labels at the top tells us an assortment of things. The "Digital" on the bottom row is almost redundant since we have the specific digital input identified below it, but it does come in handy when there's no actual input signal (it flashes to say "help! no data!"). The "PCM" indicators tells you when you have PCM, of course, which will be useful for figuring out when the HDTV is doing some decoding internally and generating PCM stereo from what should be a DD or DTS source. The "Digital" next to "Dolby" tells you that you have a DD source of some sort when it and "Dolby" are both lit.

http://www.ac3filter.net/forum/viewtopic.php?t=10

That's a very helpful explanation of SPDIF and PC audio. I will try the AC3Filter and see if it can encode game audio before sending it out to the 990.

Hi Fatawan,
I have on my ATI HDTV tuner card something called...
Cyberlink audio renderer...which basically down-mixes or passes through all digital audio through my spdf optical...when set to pass through...DTS and Dolby Digital signals are sent uncompressed to my 1070....
I have the Realtek HD audio alc882...which is 7.1
but unlike yours doesn't deal with Dolby Digital...maybe your answer lies there...

I think my only "issue" is not mine, but that of Battlefield 2. It handles surround in an odd way. Some hardware just does not work with it. The ones that do seem to be only able to provide 5.1 via the analog outs on sound cards. My DVDs play with DTS or DD 5.1 no problem. All TV has been PCM/Dolby prologic IIx. Do any of the networks actually broadcast DD 5.1? I have been watching the various shows, even things like 24, and it never changes from PCM/DPL IIx. I use an OTA antenna for HD.