This is my theater/listening room. There are couches on both sides now blocking the primary reflection points on the side walls. The rug takes care of primary reflection off the floor, and the vaulted ceiling prevents reflections from above.
These statements along with many others in your post is based on a few isolated facts, some other incorrect facts and all joined together with logical assumption. Unfortunately, by missing many pertinent facts and incorporating some incorrect facts, the logic of your assumptions cease to be logical and you end up with illogical and incorrect conclusions. I'm not trying to be insulting here bigshot, just illustrate for the benefit of others why some of your opinions and advice may not be applicable to them. Let me give you a few examples starting with what I've quoted:
Your couches are most definitely not blocking the primary reflection points on the side walls! They are absorbing some frequencies, transparent to other frequencies and reflecting still others and, they are only covering part of the primary reflection points due to their limited height. Depending on the deviation (from flat) your reflection points are creating, depends on whether your couches are helping the room's acoustics, or not. As a generalisation for most living spaces, couches placed as you have done will create an overall improvement, possibly a significant one but it won't solve all the problems and could make some of the problems worse. This is why recording studios and cinemas use specific types of acoustic treatments rather than just nailing couches all over the walls! Also, the rug on the floor most certainly does not "take care" of the primary reflections from the floor. Being relatively thin, it will reduce
some of the reflections within a limited range of frequencies, most likely in the mid-high frequency range. It will be almost entirely transparent to many frequencies, including most of the more problematic frequencies in the low and low-mid frequencies. Again, it will almost certainly be better than just having a bare wooden floor and no rug, but it's a relatively small incremental improvement in your floor's reflective properties rather than a "taking care of". Your vaulted ceiling also does not "prevent reflections from above". It eliminates a parallel surface (with the floor) and thereby greatly reduces the likelihood of standing waves (between the floor and ceiling) but it doesn't reduce reflections, it probably increases the density of the reflections and so could be causing other acoustical problems. Again, if solving acoustic problems was as simple as a vaulted ceiling, all cinemas, control rooms and dubbing theatres would have vaulted ceilings but most/many do not.
"Just about every home theater I see pictures of on the web makes the same mistakes... Speakers flat against the side walls, flush with the front wall..." :- You are not just describing home theatres here, you are describing just about every commercial cinema and dubbing theatre on the planet because they too place their speakers on the walls and flush with the front wall. So are you right and the rest of the world is wrong or do you think it's possible there's some practical applications of room acoustics you're missing?
"Taming room acoustics isn't as complicated as people make it out to be. Like anything else, you start with the big things and work your way toward the less important things" :- But this is obviously not what you have done! What you appear to be doing is: Improve the biggest things you are able to identify by 10%, 20% or whatever is practical, then move on to the next most significant things you are able to identify and easily improve and ignore everything else. As general advice to someone who hasn't considered acoustics before and whose listening environment has to fulfil other functions, I would say what you have done is reasonably good advise and will likely result in considerable enhancement of their listening experience. But this advice will not of course result in a flat or good listening environment, just one which is more to your personal liking given your circumstances and equipment. If you are after something particularly good and accurate though, then "taming room acoustics" is far more complex than you seem to realise/appreciate.
"There is a trick to getting the same system to sound good with both movies and music using a stereo to 5:1 DSP. Movies assume a certain calibration and the decoder isn't adjustable. You are supposed to calibrate to Dolby or THX standard, the same way movie theaters do. So you start by calibrating for movies and get that right first". :- Again, what you are saying/assuming, does not correspond in anyway to what you are actually doing! Have you calibrated your front speakers to 85dBSPL(C), your rear speakers to 82dBSPL(C) with Dolby pink? Have you calibrated your sub to +10dB relative to your front speakers with an RTA? Have you applied the cinema x-curve to your room's response? Is there at least 18ft between your left front and centre speakers and do you have the appropriate baffling/isolation between all your front speakers. Are all your front speakers full range (20Hz to about 18kHz) or do you have to employ some form of bass management (which is unacceptable for Dolby of THX theatrical specs)? I think we can safely say that your system is not even vaguely in the ball park of Dolby and/or THX theatrical standards. Even if it were, it still wouldn't sound as intended, as Dolby and THX specs are designed for large room acoustics and are not applicable to small rooms/home listening environments. We also have to consider the fact that many (but not all) DVDs/Blurays are remixed specifically because home listening environments and equipment are not the same as cinemas and, films broadcast on TV often have another remix again. And lastly, I hope it's obvious after this, that a system which is well calibrated for movies is not flat or balanced appropriately for the ideal playback of music in 5.1. If it appears that it is, that's a fair indication that something is wrong somewhere in the calibration!
"Also *directionality* of sound and three dimensional phase are more important than anyone realized back in 1952 when the stereo standard were established. Just like stereo improves both music and movies, 5:1 is a huge leap forward for both too. You don't know until you hear it." :- I think the importance of phase and directionality were well realised in the 50's but it's certainly NOT correct to say that stereo improves movies, it doesn't, it makes them worse! So much so, that stereo has never been one of the accepted audio formats for movies and indeed, it's not even possible to put stereo sound on the standard digital movie distribution format (DCP)! 5.1 was certainly an improvement over the LCRS format it replaced but it's not the huge leap you are stating and of course 5.1 itself has now been superseded by another step forward, with systems such as Dolby Atmos. BTW, careful about saying things like "you won't know until you hear it", as you don't know what I've heard or what I'm used to hearing!
"When I play 2 channel music through the DSP, the soundstage spreads out from wall to wall with no dropouts in the middle (try to do that with two speakers!) and it extends into the room about six or seven feet or so from the front wall." :- OK, this is particularly troubling! There should absolutely not be any dropouts or even the slightest loss in the middle with a stereo system. What you are describing is either a fault/incorrect setting with the stereo panning law of your amp or far more likely, some fairly serious phase issues between the left and right speakers (and/or the room acoustics). Amp DSP effects use phasing/reverb as part of their processing, this is corroborated by the fact that you describe the sound as extending into the room by 6 or 7 feet. A phase based effect is by far the most obvious explanation of this observed phenomena. You also mention the separation being wider than the speakers themselves and as phasing effects are the only way to achieve this, I think we can say with a high degree of certainty that your DSP is using some form of phasing in it's processing. It's not entirely uncommon in some music production to use similar phased based effects to create a stereo image wider than the speaker placement. However, it's generally avoided because: 1. When played back on a mono device there is virtually always considerable phase cancellation and 2. Even in stereo the results frequently don't work as intended because they depend on good speaker placement and relatively little phase discrepancies in the playback chain/environment.
At an educated guess, it would appear that you have got some quite serious phase issues in your room. Applying the DSP effects in your amp has altered the phase of your outputs which has changed the phase relationship in your room and evidently reduced at least some of your room's/system's phase issues. I could be wrong, but I don't believe the DSP in your amp is designed to make the sound stage appear wider or extend 6 or 7 feet into the room, as both (and particularly that latter) would be fairly unpredictable from room to room and system to system. It's likely just a consequence of the DSP phasing interacting with the phase issues in your room which is causing this effect. This would explain why the precise balancing and tweaking of your system makes such a significant difference and why you are hearing a distinct improvement in clarity and positioning when engaging the DSP. Normally the applying of amp DSP effects would cause different phenomena from the ones you are describing and exactly the opposite in some cases! It would also explain your observations when listening in standard stereo, as well as most of your other related comments, such as your perceived improvements not being present unless the right balance/EQ is applied to each speaker.
If I am correct (and you have supplied quite a bit of evidence to suggest that I am), then many of your assumptions and a fair amount of the opinions and advice you have provided in this thread will only be applicable to you and the current state of your listening environment. It's almost certain that if your phase issues could be accurately identified and solved that your opinions (and future advice) would change significantly.
I'd love to "Come by and hear it some time!", I'd like you to hear my environment too, unfortunately that's not practical due to my current location. I'd post a picture of my room but most of what's there would not be obvious from a photo and I wouldn't want my posts or this thread to descend into a "mine is better than yours" debate, even though we are admittedly already quite a way off topic!
G