I think that maybe one of the sticking points for the OP is the whole matter of why, most of the time, in a blind listening test, people - even experienced listeners - can't tell the difference between a $500 receiver and a $2000 receiver. The OP asked that in the beginning, but it wasn't really answered - at least not in this thread
The whole thing about features - that's pretty easy to understand, I think. You want Audyssey MultEQ XT32? That's a very nice, but very specific feature, and you'll have to spend at least $750 for a fully authorized refurbished Onkyo TX-NR818 from accessories4less in order to get it! Plain and simple. Right now, there's no less expensive option for that one, specific feature if you want it. So I think that's very easy to understand.
But when it comes to the matter of HEARING the difference - and when we're not just talking about features like room correction, EQ or listening modes, here's the skinny:
The vast majority of the time, we are only using 10 Watts or less per speaker - and much of the time, only 2 or 3 speakers out of 5 or 7 are even playing! Many, many folks do not realize just how little power is actually being used
most of the time.
It's only in rare - and typically very brief - circumstances where the power demands skyrocket. So it's only in these rare and brief moments that more powerful and/or higher quality amplifiers will reveal their superiority vs. the amps you'd find in a $500 AV Receiver.
Most speakers have an efficiency around 87dB / 1 Watt / 1 meter. Some speakers are less efficient. Some are more efficient. But that's about average in a lot of cases.
So what does that mean, exactly? Well, it means that if you're sitting 1 meter (about 3 feet) away from the speaker, it only takes 1 Watt of power to produce a Sound Pressure Level (SPL) of 87dB. That's loud! Full THX Reference level calls for 85dB average sound levels with 105dB peaks. That's full blown movie theater loudness. Most folks, when they're at home, prefer quieter listening levels than what you get at the movie theater. Most people prefer something around 75dB average with 95dB peaks. And many people listen even quieter than that.
So we know that if we're out in a wide open field, every time we double our distance from a sound source, we lose 6dB in SPL. In a typical room inside a house though, every time we double our distance, we lose more like 3dB in SPL, not the full 6dB.
So let's double our distance from the speaker, and then double it again. Now we're 4 meters away instead of 1 meter (about 12 feet away instead of 3). By doubling our distance, and then doubling it again, we've lost about 6dB in SPL. If we were out in a wide open field, we'd have lost 12dB. But inside a house, it's closer to 6dB quieter from this 4 meter distance.
So it still takes only 1 Watt to make that speaker produce 81dB of output, even at this 4 meter distance! That's still louder than what most people prefer at home. And even if we want to hit THX Reference Volume, we only need to double the power to add 3dB in SPL. So just 2 Watts gets us very close to 85dB Reference Volume levels from a full 4 meters away. Now you can see why, the vast majority of the time, we just don't need very much amplifier power!
Any half decent amp can produce 2 Watts per speaker. Even if all 7 speakers are being told to play equally loud at the exact same time (which almost never happens in a real soundtrack!), we're only talking about 14 Watts total! And that's if all 7 speakers are a full 4 meters away from the listening position. AND you're listening at "movie theater loud" 84dB SPL!
Even if your speakers are a lower, 4 ohm design, any decent $500 AV Receiver should be able to muster up 14 Watts. So that is why, most of the time, no one can tell the difference between a $500 receiver and a $2000 receiver - or $10,000 in separate amps, or what-have-you. We just don't need very many Watts!
BUT, things change VERY rapidly. For every 3dB increase in SPL, we have to DOUBLE the power. For every 10dB increase, we have to multiply the power demands by 10x !
So let's just imagine that 2 Watts is giving up 85dB of output from 4 meters away. That would be the case with 88dB / 1 Watt / 1 meter efficient speakers. We lost 6dB in SPL by doubling the distance, and then doubling it again. Then we increased the SPL 3dB by doubling the power.
Now it's time to hit those 105dB THX Reference Volume peaks. Multiply the power by 10x. That gives up 20Watts per speaker, and results in 95dB in SPL. 10x the power equals 10dB increase in SPL. Now we need 10x more power again! We've just hit 200 Watts all of a sudden! And now we're at 105dB.
That didn't take much to suddenly be calling for 200 Watts per speaker, did it? And what if your speakers are less efficient? Or you're sitting even farther away? A mere 3dB difference will call for a doubling of the power again. Now we're talking about 400 Watts in no time! And it just goes up exponentially from there.
In truth, AV Receivers aren't a good way of trying to get massive Wattage capabilities. The TX-NR818, for example, might claim 135 Watts/channel. But that's only with 2-channels driven. So that tells you how many Watts the power section of that AV Receiver can really supply, which is about 270 Watts total. If all 7 channels happen to call for the same amount of power at the same time (again, not something that ever happens in real life, but this is just a hypothetical), then the TX-NR818 becomes a 38.5 Watts/channel amplifier, NOT a 135 Watts/channel amp, like the spec sheet says
The dynamic power rating into 1 channel also lets us know a little something about the capabilities of each individual channel's output transistors. In this case, even though the power section of the TX-NR818 can deliver around 270 Watts total, each individual channel has a maximum output of 150 Watts, at which point, the output transistors of that one channel become saturated and cannot deliver any more power. It's a bit like plumbing. You've got this 270 Watt "bucket" of power at any given moment. But all of that water has to come out of a nozzle. If you open all 7 nozzles, each nozzle can have 38.5 Watts, but if you open just one nozzle, that nozzle becomes the bottle neck, and it can only let out 150 Watts at a time, not the full 270 Watt "bucket".
Things get a little more complicated when we bring the impedance of the speakers into the mix. In this analogy, we're basically connecting a hose to the nozzle. And "easier" 8 ohm speaker will be a somewhat skinny hose. A "harder to drive" 4 ohm speaker will be a fatter hose. If the hose is fatter than the nozzle, we've got a problem. The nozzle can't feed the fat hose fast enough - and that's what happens to low cost, or lower quality amplifiers when they're connected to low impedance speakers. They've got a skinny nozzle, the speakers have a fat hose, so they "starve" for power, even if the "bucket" of Watts is about the same size.
So what do more expensive AV Receivers give you vs. less expensive ones? The most obvious things are features and inputs - and that's really what you should base your decision on. You MIGHT also get fatter "nozzles" that can handle the fatter "hoses" of low impedance speakers. But even that is not always the case. And, in truth, you'll get a bigger "bucket" of Watts, but not THAT much bigger. You might go from a 180 Watt "bucket" to a 270 Watt "bucket". But remember that double the Watts only gets you 3dB more output!
So it's not really about the Watts. And since we only use 2 Watts/speaker or less the vast majority of the time - maybe 10 or 20 Watts per speaker for some big crescendos and explosions - we're just not going to HEAR a difference. If you sit far away, have difficult to power speakers, have very inefficient speakers, or you just want to hit full THX Reference Volume levels, then you might suddenly be calling for 200 or 400 Watts per speaker or more! NO AV Receiver - no matter how expensive - is going to deliver THAT. So if those are your circumstances, it's time to get some external amplification!
I hope that helps and clears things up for some folks
