You guys wonder how the soundtrack was originally recorded or restored, whatever the case may be. But I am thinking about it from the perspective that these avr's are usually supposed to simulate surround sound if the audio is not encoded with it. I am not sure what dsp programs are meant to do that. Maybe any and all? Or just Nueral X?
You have to understand what these sound modes are intended to do. The first issue is if that most recordings have a soundfield originating from straight ahead. So the rest is ambient field from wall and ceiling reflections. It is this ambient field that gives the sense of the space you are in.
Obviously the front/forward field is much louder than the ambient field, unless the performers were recorded in a concrete public lavatory.
Now when you make a recording, particularly if you record at some distance, then the mics will pick up the forward field (direct) and the ambient field. This ambient field will be awash in complex phase/time shifts. Remember phase shifts can e expressed in time or as degrees of divergence. The only thing important to understand about this is that they are different ways of expressing exactly the same thing!
Now in a 2 channel recording with spaced or coincident microphones, you will record the forward and ambient fields simultaneously. And they will be reproduced from the front pair of speakers simultaneously.
Now what these up mixers attempt to do, with varying success, is to sort out direction and time, from the phase changes in the ambient field from the first arriving direct field signals. They do this with varying degrees of success.
From my evaluation the only ones worth the time of day are from Dolby. My favorite so far is DDDSur. In my view that is the only one that is any good, and on a lot of sources it is very good indeed.
Now, the ear is not easily fooled, and direct and reverberant field need to match for it to work properly. That means all speakers must be of similar quality and have tonal footprint that matches. So, the idea you can use speakers of inferior quality for the surrounds and rear backs, compared to the front filed is false. Results will be suboptimal if that is the case.
This is where I'm lucky, as I make my own speakers and I'm a hoarder. My rear backs are my studio monitors that musicians, conductors used to use to choose their takes in my recording days. My surrounds are the location monitors I used to use when I was making regular broadcasts for the local public radio station. So all the speakers are tonally very similar indeed. In that regard I am unusually fortunate.
Now the final issue and problem is how the recording was originally recorded. These upmixers work well with classical choral and operatic program, but poorly for works in the popular domain.
In the pop/rock domain, instruments are close miked and artificial reverb used extensively. So when engineers from a session in a local studio come here to check a mix, just the right and left main speakers are used, otherwise it really sounds pretty awful.
In the classical domain using lots of microphones tend to negate a good result from upmixers. I personally never used to do that.
I do know from watching AV classical streams, that there is now a very welcome trend to use less microphones and place spots more distantly.
I would sight the Detroit Symphony Orchestra productions specifically, where they are using straight Decca Tree and soloist spotted gently with the mic at a greater distance than normal. This captures the wonderful acoustic of their hall spectacularly.
When you analyse these issues in WaveLab screens you can see why this is so.
Classical/opera recordings are awash in the ambient field with a screen busy with exotic circular dancing lines. Whereas recordings from the popular/rock domain have lined largely centered up and down. You can tell by looking at the screen that these are essentially a bunch of combined mono recordings, which of course they are. So the upmixer does not really stand a chance.
Since you live close by, I can show you the various upmixers in my Marantz AVP and also show you WaveLab screens on the DAW.
