Originally Posted by chriscalvert
I need to add a little more information here to explain what I want to do and why and some of this is based on stuff I have read since my original post.
Whatever I end up with has to be wife proof. I still haven't managed to get her to hold the Harmony One steady when she turns the system on. Incidentally the remote works much better now that I sequenced power on from the sink back through to the source.
I found a device called Delock HDMI Stereo / 5.1 Channel Audio Extractor. The blurb says "the audio signal can be sent digital (S/PDIF) and analog (stereo) to other devices such as headphones or a surround receiver." And it is HDCP compliant. Switchable between stereo and 5.1 channel. If it is HDCP compliant I have to presume that whatever you set the switch to will be reflected back to the source
I'm not sure you are completely understanding what you are trying to do. HDCP has nothing to do with this other than if you aren't HDCP compliant you won't get any signal, video or audio.
The EDID handshake is what sets whether the source sends stereo or 5.1-channel or 7.1-channel. The EDID goes from sink to source. The audio and video signals are sent from the source to the preamp to the sink, but the EDID goes the other way from sink to the preamp (who modifies the audio parameters) then to the source.
But, the most important thing to remember is that you can only have one audio stream at a given time. So, once the source is sending 5.1-channel out, there is no way to also send stereo out.
As you pointed out converting 5.1-channel analog to 2-channel analog is a valid way to add a stereo output. To do that you would have to downmix, using some variety of mixer, all six channels of the 5.1-channel output into stereo. The difficulty of this is that you have to know how much of each channel to add together, although simply adding each channel at the same level can produce a rough approximation of what the stereo stream should be.
I say rough because the Dolby Digital, TrueHD and DTS-HD MA (but not regular DTS) source programs all carry what is called "downmix coefficients". These tell a decoder that if they are converting to stereo to set each channel to these individual levels. One big thing the downmix coefficients do is to prevent clipping (or at least they are supposed to) since combining 3 or 4 channels into one channel can result in a signal that is too loud for the preamp to decode properly. The coefficients also keep the back channels and LFE from being too loud when converted to stereo.
Unfortunately, once you convert to analog those downmix coefficients are lost.
Why not just use the front left and front right channels to send to the other TV? I'll use (strangely enough) NBC Nightly News as an example. When Brian Williams is talking, his microphone is sent over the center channel only. When commercials are played their dialog is usually but not always sent over the left and right front channels with the center just used for effects. So, if you just use the front left and front right, then you would not hear Brian Williams at all but you would hear the commercials in all their glory. So, you do have to mix all 6 channels to get a valid stereo output.
So, you'll need something that mixes the channels together. I have used an old Marantz AV560 pre-amp to do that from a digital signal. So, basically convert the HDMI signal to digital S/PDIF (as you wrote) and then send the S/PDIF signal to another pre-amp to convert to stereo. Then re-combine that audio with the video and send to the stereo TV over HDMI. Hope "like heck" that the audio and video are synced properly since I'm not sure you could fix that if they aren't. The AV560 doesn't exist anymore but many current receivers will downmix S/PDIF into 2-channel.
Your DVI suggestion is interesting. If your stereo TV has an S/PDIF input (some have S/PDIF outputs but not inputs), you could send the S/PDIF output to the TV directly with the video coming by DVI (which is the same video signal as HDMI). If the TV can convert 5.1-channel to stereo, you are set. If not then if your HDMI to S/PDIF converter doesn't change the EDID (most do) to stereo, then you would be set. But you would have to check carefully since many of these adapter do their "downmix" by telling the source to just send stereo when you flip the 5.1-channel switch to stereo. In other words, the device doesn't actually downmix but just tells the source to do it instead. In that case your pre-amp would also see stereo instead of 5.1-channel audio.
The webpage for the device you referenced says, "Switchable between stereo and 5.1 channel". It says nothing about being able to do both simultaneously. It also does not reference TrueHD or DTS-HD MA, which might mean that a Blu-Ray player will only send Dolby Digital or regular DTS if connected to that device. You might want to check with the manufacturer before purchasing to see the limitations.
Of course, if your present pre-amp already downmixes while outputting 5.1-channel audio over the speakers, then all you would have to do is to re-combine (re-inject) the audio into the video signal.
Either way you are looking at more little boxes and probably between $100 and $600 to do this, depending upon your current pre-amps capabilities.
It is still easier (and more cost effective) to do all of this at the sources and then send that as a separate audio signal. Unfortunately I understand that running extra cables can be difficult in many pre-existing installs.
This all goes back to only one audio stream at a time over HDMI.