You cannot compare iems using balanced armature full sized speakers. You just have little experience with very sensitive iems, it's nothing hard to believe. Single balanced armatures can have wild impedance swings all by themselves. Combine that with multiple armatures and crossovers and you can get some pretty varying impedance curves. Manufacturers only state the rating at 1k for standardized specs but the truth is, it can vary heavily at any other point on the frequency response. Campfire isn't the only one making super sensitive iems; Shure, Empire Ears, Ultimate Ears, Jerry Harvey Audio, well you get the picture. If you want to read more on the varying effects of impedance on balanced armature iems (small dynamics in iems tend to have flat impedance responses), you can check out Rin Choi's blog. While he hasn't updated it in ages, it's a great library of information: http://rinchoi.blogspot.com/2010/05/determining-very-dbspl-coming-out-of.html?m=1 Just check out any iem measurements made with armatures. He'll often show varrying frequency response measurements with adding 10, 33, 50, 100 ohms; possibly even recommend an impedance value to bring the iem response closer to a measurable neutral response. The output impedance of a given dap or amp can be dependent upon the opamp used, some require more output impedance. A designer might prefer the sound of certain opamps; output impedance be damned. Sometimes it's just the circuit design of the engineer. Apple has had iPhones under 1 ohm, around 2 ohms and around 3. I'm not an electrical engineer, so I can't tell you why they change the design each model for differing output Z but you can't necessarily consider a few ohms a fail, if you don't know their design target. Most portable and full size headphones can take higher amounts of impedance before they are affected but as an iem user, it would sure make my life easier if everything was 1 ohm or less.