roskodan
Headphoneus Supremus
I can't say why the A2C sounds bad and why the Ether 2 sounds good with the RNHP. What sounds good and what sounds bad is fairly relative from person to person. I will go over the RNHP specs below.
Looking at the manual sheet for the RNHP provided by roskodan, and doing a little bit of calculation, I would think that the RNHP has enough voltage AND current output to make the A2C reach about 110dB without missing out on dynamic range.
Using this measurement as reference: 16 Ω typical Load: 1.933 VAC RMS @1kHz = 230mW RMS
This would mean that for a 13 ohm load, the RNHP would have roughly around 2.379 VAC RMS @1kHz = 283mW RMS
Doing a reverse calculation of power with the VAC provided, you would have about 118mA current feed to the A2C, which is plenty of headroom given that it requires around 20mA to reach 100dB SPL for the A2C (using this as reference: http://www.digizoid.com/power.php)
Unless I'm missing something in viewing this, I would think the RNHP has enough voltage and current output to drive the A2C. I welcome someone else to correct my assumptions here.
You need to notice the main feature. Power falls on the RNHP from 44 Ohms down. So the power is lower at 13 ohms. Which means the RNHP is heavily current limited. Which is a huge problem for such headphones as MrSpeakers. Also that is probably the combined power output, as it's not specified per channel, so got to halve whatever figure you calculate.
Also those power rating are useless without distortion figures.
But the main problem is current limiting. The amp losing power at lower loads.
It may sound good, gotta try it to know it. However I wouldn't bet on it, especially since the member in question reported a disappointing performance. And also based on my experience with many other amps.
And the headphone in question is the AFC2.