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What I am trying to find out is what the svs does with its down-mix.2ch analog stereo for use with headphones.
So can you please explain how the svs down-mixes and why its better than anything for 2ch analog headphones and down-mixing?
Just to be sure you are clear on what the Realiser is trying to accomplish, and why it is actually a completely different product than any Dolby Headphone or similar implementation of "virtual surround sound" via headphones.
As was stated by Edwood, the product is first of all attempting to literally capture (i.e. "photograph" with calibration microphones inserted in YOUR own two ears) the acoustic signature of a listening environment, and store that measurement in a file called a PRIR. Everything about that small or large room (or theater or auditorium, for that matter) which makes up how the calibration sweep signals are received inside YOUR own two ears and "how it actually sounds to you", is what makes up the essence of that PRIR. EVERYTHING IN THE ENVIRONMENT is captured and recorded (like an EKG), and it thus reflects the speakers used and their placement, the electronics and amplification system and interconnects, the carpeting (or lack of it) and audio baffles on walls and ceilings, etc.
So the purpose of the PRIR is to try and capture exactly how a given listening environment SOUNDS TO YOUR EARS. Nobody else's ears, and no multi-channel source like a movie or HD-audio. The purpose of the PRIR is simply to digitize exactly how your ears and brain take in sound in that particular room environment.
Why is this the goal of the PRIR? Because the goal of the Realiser is TO DUPLICATE THAT SOUND NO MATTER WHAT THE EVENTUAL SOURCE SIGNAL IS!! In other words, listening to any future source (be it mono, 2-channel, or multi-channel) played through the Realiser and headphones/amp SHOULD SOUND TO YOUR EARS EXACTLY AS IF YOU WERE IN THE ORIGINAL LISTENING ROOM ENVIRONMENT HEARING THAT SAME SOURCE PLAYED THROUGH THAT ROOM'S ACTUAL SPEAKERS.
In fact, that is also part of the calibration/measurement ritual... at the end you do an A/B test putting on the headphones and then taking them off, and inevitably marveling at how indistinguishable they seem to be. Even though we all know they're just two headphones (being fed by an analog 2-channel signal coming out a some kind of A/D/A processor) feeding our two ears with a 2-channel audio, somehow we seem to get the exact same (a) "virtual speaker" placement illusion, both horizontal and vertical from where we're seated, and (b) tonal/volume equivalence with the true loudspeakers.
In other words, listening to any source through the headphones fed by the Realiser is truly the same (to our ears and brains) as if we were in that listening environment and hearing the same source through those real loudspeakers.
That's the goal of the product. The goal is not to take an arbitrary multi-channel or 2-channel source and provide some magic "virtual surround" through headphones that everybody will experience exactly the same way and say "WOW!!!". The Realiser experience is an individual one, since I hear sound with my ears and skull and brain differently than you hear exactly the same sound. So you have your PRIR and I have my PRIR, both separately measured in the identical listening room environment. And when used for playback through the Realiser and your headphones, you will hear a "duplicate" of the measured room as that source would have sounded to you if played in that room. Same for me... but our PRIR's are distinctly different.
Now there are a few more details, like the second HPEQ file which measures how your headphone/amp sound TO YOUR OWN EARS (again measured using the calibration microphones and calibrated sweep signals, to define a proper EQ curve which will be blended in with the processing of the PRIR at playback time).
So... the PRIR measures how that particular room/electronics sound to your ears. And the HPEQ measures how your headphone/amp sound to your ears, no matter what the source. Combining the two measurements in reverse, used as a "filter" by which all source (mono, stereo, or multi-channel) can be played and output through your own personal headphone/amp to your own two ears will optimally duplicate exactly how that source would have sounded to those same two ears you have in that particular listening environment.
It's not Dolby Headphone or a downmix of multi-channel to 2-channel stereo to provide a sensation or illusion of virtual surround. It (along with the PRIR and HPEQ measurement files, both of which are completely individualized to your own ears) is a device by which an acoustic "filter" of a listening environment can be fabricated and used to play back any source through headphones so that you believe you are listening to that source in the very original listening environment through its true loudspeakers (as measured in THAT listening environment through THAT PRIR file).
Note that you can take exactly the same source (e.g. BD of "Avatar") and play it back through the Realiser using two or three different PRIR's (all of which represent how YOUR ears and body and brain heard sound in two or three different audio studios or listening rooms), and the exact same source will sound quite different... as it should. Because the Realiser is NOT trying to give you a "best possible multi-channel virtual surround sensation" for any given source signal. It is trying to duplicate a listening environment no matter what the source signal is that's played through the PRIR/HPEQ "filter". So just as three different audio rooms will sound different to you if you took the same BD movie to each room as a test, so will playing a constant source back through three different PRIR's (each of which defines a unique listening environment) sound different to you. No one is right or wrong, but you'll no doubt eventually settle on which one "you like better" or that "sounds the best to you" and will no doubt eventually "pick that listening environment for all of your listening experiences" going forward.
I happen to agree with Edwood, that my AIX 5.1 PRIR is actually now my one-and-only "listening environment" that I use for EVERYTHING 5.1 (and 2-channel as well, actually)! I have an AIX 7.1 PRIR as well but don't hardly get to use it. What's most important, however, is that the acoustic characteristics of that AIX studio room in which we were lucky enough to have been allowed to get PRIR files calibrated make it possible for us to essentially have a $100K or more audio system in our Realiser/headphones... to listen to any source through. It's like we went to AIX every time we watched/listened to HDTV or a BD movie and were once again thrilled to hear sound in that wonderful studio. But it's in our headphones, to our ears, in our bedrooms.
