I never understand these explanations, remember that I am a noob when it comes to audio, I only recommended the amplifiers of the Garage 1217 because I did not see sense in buying an amplifier like the WA22 for example that costs thousands of dollars to to drive IEMs when there are portable amplifiers like the OPPO HA-2 or the Chord Mojo, which is why I recommended them because they are much cheaper and have this ability to change the output resistance.
First, apart from the cost of the WA22 the real issue with an amp like that being used for IEMs is that it's HUMONGUOUS. It can't even just do well on just any desktop set-up as it's practically the size of a speaker amplifier.
Second, it's alright if you don't understand the explanation (though I'm not sure how to simplify that apart from just going into further detail, which could be even more of an impediment to understanding it) and you're admittedly a noob, then why recommend something for technical reasons you do not sufficiently understand? That will be like, if this was a computer forum, someone asks for what parts to get to play Total War with some light media editing work, and you suggest a G4562 and blow all the money on a GPU just because reviews keep saying that CPU doesn't matter as much when 1) he'll have light workstation tasks running on it and 2) reviewers don't even use Total War and have no numbers to back up the claim that the CPU barely matters (by now even GTA V and Assassin's Creed are showing that CPU core count as well as single core computer performance matters).
Now, to go into further detail on impedance, the
very general rule is that the ratio of the load impedance (this is the headphone) to the output impedance (on the amp) needs to be roughly 8:1. I say "general" and "roughly" because 1) unless you understand and do the math, this is just a shorthand for getting a safe number; which is because 2) the effect varies not just in terms of absolute ratios but how high the impedances are since the same ratio for low and high impedance loads will not necessarily have the same effect and 3) even the specs of the headphone and amp can affect what kind of sound shaping will occur as some headphones can end up sounding very different on two otherwise similar topology and high output impedance amp designs (K701 will sound slightly warmer on DV336, but like a tin can on a Little Dot MkII).
Again, and his is something I already put in the prior post, if you start out with an amp that has a low output impedance in the first place, then it will run
any impedance properly at least as far as impedance is concerned (output power, distortion+noise levels, and gain are another matter). A variable output impedance is
not required to run different impedance loads properly, and by "properly" I mean "does not introduce any changes to the input signal apart from amplifying it into a stronger signal to move the transducers." If you are starting out with a low output impedance amp then it will not reshape the signal and the amplifier does exactly as it's supposed to do.
Reshaping the frequency response in most cases is just more easily done with EQ anyway since you'd have more control, especially with digital EQs and computer sources that are more commonly used now. For example even if you can use a high output impedance and gut lucky enough that it boosts the bass and rolls off the treble on a given low impedance headphoone/IEM (or boosts midrange and rolls off treble on a high impedance headphone), that tends to have a very wide but generally more uniform effect. If the problem with a particularly bright headphone for example is that it has a peak somewhere between 4000hz and 10,000hz, this kind of EQ effect reduces everything in that range, but you're still going to get left with a relative peak in that range, which you could have just trimmed in a more precise (and to a point, surgical) manner by using an equalizer with variable settings.
