Originally Posted by chris_h2
I know my TV does pass thru DD5.1 from HDMI to the optical output. It's working for the DVD player, and also used to work from a D* HR-20 (prior to my moving a few months ago).
This is a more complex issue that it might seem on the surface.
The Moto boxes (DCT/DCH/DCX) have digital audio delivered out either from (a) HDMI, or (b) optical/coax.
The fact is that the digital audio out of optical/coax on the DVR will ALWAYS be the true underlying audio program from the content provider. It will ALWAYS be DD5.1 if the program is delivering DD5.1 audio. There's no way to prevent that. If you use optical from DVR to AVR then you will ALWAYS get the multi-channel digital audio program sent from DVR to AVR, as provided in the source program's content.
In contrast, the digital audio delivered over HDMI (either direct to HDTV if you use the HDTV's speakers, or relayed through AVR where it can be "tapped", decoded, and delivered to your multi-speaker sound system via your AVR so that your HDTV's speakers are typically disabled even though there is an HDMI relay from AVR to HDTV for video use only) is subject to a variety of factors.
In particular, the nature of the digital audio delivered from DVR to a receiving device via HDMI will be governed by the "Additional HDMI settings" of the DVR, which has three options: (a) AUTO, which lets the receiving device tell the DVR what type of digital audio it can accept via HDMI as determined by the HDMI handshake between the two devices, (b) L-PCM, which forces decoded 2-channel L/R digital PCM stereo to be delivered from DVR to the device, or (c) PASS-THROUGH, which simply sends whatever the digital audio program is in the source content from DVR to receiving device, no matter whether or not the receiving device can actually accept it successfully in that form (though it may be able to pass it on further, even if the HDTV itself cannot really handle it internally).
Now most HDTV's CANNOT accept DD5.1 digital audio, since most HDTV's do not have more than 2 speakers anyway and certainly do not contain a built-in Dolby Digital audio decoder. So in the HDMI handshake between most HDTV's and these DVR's, the HDTV says "I cannot accept DD5.1, so don't send it to me. Instead send me decoded 2-channel digital PCM stereo for the audio program." And that's what the DVR will send, if you have the "AUTO" value set in those "Additional HDMI settings"... namely only 2-channel stereo delivered over the direct HDMI connection between DVR and HDTV. And since the HDTV is then going to receive only 2-channel stereo, that's exactly what it will pass on out its own "digital out" (e.g. your optical feed to your AVR from your HDTV).
Now if you want to FORCE DD5.1 digital audio to go from DVR to HDTV (where you will then pass it on out via optical to your AVR from HDTV), you must FORCE DD5.1 to be delivered using the "PASS-THROUGH" setting in "Additional HDMI settings", so that the DVR will simply ignore the fact that the HDTV itself cannot really accept DD5.1 but this doesn't matter because you're not using the HDTV's speakers anyway but will simply pass the delivered (and unusable by the HDTV) DD5.1 digital audio out over HDMIl to the connected HDTV and then on to the optically-conected AVR for final decoding and playing through your speakers.
So, the question is simply why do this (and require PASS-THROUGH on the DVR, which is going to be "reset" back to AUTO just like "native" gets reset back to "1080i/720p/480p" whenever there is a hiccup in the HDMI device connections)?
Why not just have an optical connection directly from DVR to AVR as has been suggested? This will then ALWAYS deliver DD5.1 from DVR to AVR, which is what you want. Then you'll only be using HDMI from DVR to HDTV for video (with speakers on the HDTV disabled). This arrangement avoids the "loss of native" problem because you're HDMI-connected directly from DVR to HDTV (though you do lose any onscreen display from the AVR while watching the DVR, unless you also have an alternate second HDMI or component video path to the HDTV coming from the AVR).
Or, you can just use HDMI from DVR to AVR and then HDMI from AVR to HDTV, dealing with any possible "loss of native" if it occurs or just using the FORMAT button to cycle through fixed resolutions as you need to. But then the AUTO setting for "Additional HDMI settings" will ALWAYS deliver the proper digital audio from program to AVR, since the AVR tells the DVR "I can accept DD5.1" in its own HDMI handshake.
Normally the AVR is the "switching box" for all audio/video source devices (including your BluRay player). Assuming it has 3 or 4 or more HDMI inputs, all of your HDMI-enabled source devices should feed your AVR via HDMI cables, providing both highest-possible quality digital audio and digital video from source device to the AVR and beyond.
There is normally never a need (or justification) for feeding audio to your AVR from optical output of the HDTV (unless you're using the built-in OTA ATSC tuner of the HDTV instead of your cable/satellite provider) and then in this special situation the HDTV is yet one more source device feeding the AVR and your sound system.
Normally, all source devices go to the AVR. And HDMI from AVR to HDTV is strictly to provide digital video.