Well Shigzeo I'm more so referring to the negative effects the higher output impedance' have on sensitive IEMs and headphones frequency responses. I tend to be a real stickler on that ever since having bad experiences with such gear. Plus I never knew why the hell I was not happy with the combo and why it all sounded weird and off. Then I found out later the reason why was the 10 ohms output impedance (Fiio E9) lol :P. So I knew something was wrong before I even knew the cause. Ever since that I've been quite vocal about this kinda stuff. I no longer buy amps that have more than 1 ohm output impedance and I sure hope the 901 gets that right this time.
Hey Lee, I use headphones and earphones interchangeable, which is my problem - something I need to fix. DFKT used 16Ω earphone loads that didn't phase the 801 at all. They aren't balanced armature earphones, but they do present quite a load. I may borrow on to test output Ω later on, but again, I assume it is quite low. High output Ω isn't its issue. It's issue is the NOS DAC that is made for living room listening via speakers, which has a rolled off high frequency plus lower overall stereo separation. Some people really like that sound, and it was designed for that sound.