The output impedance rating is the one that will deliver more power transfer.
You can connect 600 Ω speakers and it will work, but delivering much smaller power.
What's an intuitive way to think of the output impedance? Why does an amplifier even _have_ an output impedance?
Anyone who talks about the impedance of a device, MUST express "at such frequency".
It does not happen. Marketing is who usually decides publications about a product and they do not care about proper technical terms.
The impedance varies with the frequency, by its nature. The formula "impedance = function of frequency"
Change the frequency, and the impedance changes.
A plain speaker with impedance rated at 8 Ω; should had said "8 Ω at 1KHz".
But nobody cares about doing things right and learning/understanding becomes difficult due to those omissions from careless people.
About matching :
Form a cotton ball; throw it as far as you can; it will land about 4 feet away.
Make a paper ball; throw it as far as you can; it will land about 25 feet away.
Throw a tennis ball as far as you can; it will land about 100 feet away.
Throw a golf ball as far as you can; it will land about 150 feet away.
Throw a baseball as far as you can; it will land about 200 feet away.
Throw a football as far as you can; it will land about 120 feet away
Throw a basketball as far as you can; it will land about 80 feet away.
Throw a bowlingball as far as you can, it will land about 15 feet away.
Throw a lead demolition ball as far as you can, watch your feet.
Now, have the same test done with a seven year old kid:
Distances reached will diminish accordingly to the strenght of the kid.-
What is going on ?
It is not the lightest nor the heaviest the one that got the farthest away.
It is not the lightest nor the heaviest the one that used up the full strenght
CAPABILITY of the arm muscles.
It is the one that MATCHES the arm strenght. There is one object
that flew the farthest for each person... you ; the kid.
When a rf or audio amplifier drive an antenna or a speaker or a
subsequent load, there will be an optimum FORCE -TO- LOAD ratio
that will deliver the most POWER. That load will not be a tiny nor a huge one.
A rated power output is the capability of a certain device AT a given
impedance load.
Unmatched driver-to-driven does NOT mean that there will be no action.
Your 400 watt stereo will burn yours ears off at full volume knob through
headphones but will be delivering only a couple of watts power, not
the 400 rated watts... because your headphones impedance is 600 ohms
instead of the at-rated 4 ohms... it is like the grown up throwing the paper ball.
As mismatch extremes, it is possible to push a ship by swimming,
or use a bulldozer to tow a bicycle.