They say that most of the Chi-Fi will have a high output impedance. If its using the TPA6120 then its a sure thing, unless they state otherwise. Generally speaking if a product/manufacturer has low output impedance they will be bragging about it, or so im told. Look at the FiiO K5 they clearly indicate that they have <1 Ohm on their website, same thing with the Objective 2 Amp, etc Then compare it to SMSL PHA, SMSL M6, FX Audio DAC X6/X7, Topping A30.... no info even if you message them on their website.
Planar Magnetic headphones are not as sensitive to output impedance compared to Dynamic, again, as I have read. Output Impedance affects the dampening factor or the movement of the speaker diaphragm, which is not a thing for Planars because of how they produce sound compared to Dyanamic drivers.
So, I totally messed this explanation, but definitely do your own research as others will explain this more coherently than I will ever be able to do so.