This is where I found the measurement:
https://www.soundstagenetwork.com/measurements/atmasphere_ma1_mkii2/
This seems much different from what is on the website for the product, 2.3 ohms.
Frequency response with a dummy load in green. I think that is referring to the Ken Kantor circuit which simulates an 8 ohm two way but I would not have expected that dip at 4KHz. The magenta line is no load. The blue line is 8 ohms. There is a 7db difference. That requires an output resistance > 8 ohms.