speaker efficiencey?? Starting point...? 92db??

There is nothing complicated about a 92 db speaker possibly falling within perfect range of a basic surround receiver not needing to be adjusted, as he stated a few speakers were dead on without moving channel levels. 92 db happened to make this occur, if they were 88 db, it would guarantee with that speaker the levels would be moved up a bit, and with 96 db speakers probably would have been well over the 75 db benchmark making those levels back off into the negatives on the channel gain levels to match the master volume, thats all I was saying... And I was simply giving a little explanation to his final question SEE above not about the 92 db question, cause yes they will work fine 92 or 102 just trying to build example's to follow, but maybe not the best explanation... first post
" what exactly does the efficiency rating mean?>??"

I see where you are confused, and so am I... I kinda combined the Effectiveness of it Vs. what could happen via difference's in Db ratings, which was part 2 of the first question.. So I did over do it and should have been a little more clear on the basic question and ended up answering as one reasoning behind the theory. Sorry, sometimes I write half and come back while at work on the computer then submit the post, thoughts float around and not always land in the right spot.

Don't get so hung up on the efficiency rating of the speaker...the main thing to look for is it's nominal impedance and is it stable at that number...if the speaker has a higher impedance, low 90's like a Martin Logan but goes down to 2 ohms then you need a high current design amp that doubles down power as the impedance drops.
Larry

I would say that the relative levels of the individual channels and how closely they match one another has absolutely nothing to do with the system's ability to provide flat frequency response. That would be a whole different topic and to measure it you'd need test tones recorded at identical volume throughout the audible frequency range, and an SPL meter to chart the results.

Most combinations of rooms and speakers virtually guarantee that the frequency response arriving at your ears will deviate quite a bit from "flat." Then again, if it actually measured flat (nearly impossible without EQ) it would sound way too bright to those with normal high-frequency hearing ability.

A gradual rolloff in the lower high frequencies (probably with some degree of boost in the upper highs) sounds "natural" to most people. And that's a whole different topic unto itself, as well. :)

Plato is right.We may be onverge where even HT recievers have room correction to flatenntheings out buit that is now perveiw of #,600 DEQX (great pre/pro),$10K TACT.Some speakers like Infinity have RABOS to take out upper bass "hump" and produce flatter response.But this strays from the question path.
92 db may mean in say 12x14 room you could get into esoteric SET (single ended triode)amps that put out 6 watts as long as you didn't want to blow walls down.But this is another application that you are not into.This efficincy means you will be happy with your 75 watts while another person with 87db speakers would crave more current.As far as what audiokenisis and Matrix were saying I have also heard room of thumb is that-every increase of 3db is like doubling power.But as Laryken points out this is speakers that are 92db with an easy load.I sold B&W for a time and even though 803Nautilus was rated at 90db effcinecy 100 quality watts (an amp stable to say 2 or 1.5 ohms).I thought 200 watts was what folks needed and if in a big room maybe 300 wats so they got CURRENT whose amps may be important than wats.The reason for this even though the speaker was rated at 90db (should be easy to drive right?) it had a nasty impedance dip down into that 2ohm or so range.I do not think that the current delivery from 75 yamaha Watts is at all close to beter made (read more expensive amp) from another company.Even when selling HT I noticed that Harmon Kardon might be rated 65 watts but was louder than a 100 watt reciver (stereo or HT ) from another mid fi brand.Not knocking Yamaha at all they introduced a lot of HT invotaions in HT reciver market and are a good choice at the asking price (which can go to $3K for a top of the line unit),But don't expect it to run like a Krell set up or any other with 200 rms and high curent delivery all around.In sum I don't think if you hear it breaking up where it shoudn't (don't expect the reciver to not distort say the cannon fire in "Last Of The Mohicans".Almost all gear will.Be reasonable).The thing is in Hifi one spec is realtive to another.Things in 70's got so bad the goverment imposed certain standards because companies were coming out with "1000 watt" audio and car gear that would play no louder than one that rated for 60 watts that kept it's ratings to an industry norm and folks complained to FTC.An easy to see example of this is speaker measurement.Measuring speaker you get much better idea on paper of what you will hear if spec is for say low freqency say 60 Hrz. is Plus or minus 2db not plus or minus 6db.Both might be "true" but you'd much rather the bass within the 2 db measurement.The goverment standards were just to keep things from getting into total BS/deceptive advertising but as wuith my comparrison of HK verus Yamaha I sold the goverment standards did not ame evryuthing "absolute" just from getting out of hand.Still you can find those 1000 watt monster amps at Costco for $89.99 so againn by empahsizing one spec while deviating from accepted norm still happens.Not sure why your meter readings trouble you(or if they do) is importanty to you as to paraphrase Duke Ellington "if it sounds good it is good"
Chazzbo