I use a very established method to measure and calculate the output impedance of all the amps I reviewed. It is calculated by measuring the unload(V) and loaded voltage(VL) with a known fixed resistance load(RL). The result is calculated from them. The formula is given as follow:
Zo = [RL ( V-VL )] / VL
Just so you know, I use the same method to calculate JDS's C421's output impedance and find out it is much higher than what JDS has listed in spec. I ran the result as well as the testing method through JDS (and John @ JDS is an electric engineer himself), which he later confirms that my result is correct and his simulation is incorrect (which is what his original output impedance rating was based on). There is a real difference between what is claimed, and what is measured.
Also, since you don't bother to read my review, the output impedance of TBH has been recalculated at 5,4ohm months ago after I get a better multimeter (which gives me more precise measurement). The new result has been updated in my thread for months, but I guess you wouldn't know. Just to be sure, I remeasure it a couple of times (even at different frequency) to confirm the latest number is correct. Still it is not a particularly low number, certainly not 0.3ohm. If HeadRoom really feels strongly that my measurement is incorrect and able to show me how the method I used is inadequate, I welcome the correction and fully apologize for what I have posted. Until then, the review will stay as they are.