Sorry, my fault.Thank for replying. the both of them I mean A30pro and L70.
I was using the Teac ud-501 many years. Now I have the thought to upgrade it.
I try to search but I can't clear understand the related calculate. (something like the impedance matching between dac and hp amp, the amp output power and hp impedance, ........)
My thought was if I use the low impedance hp connect to the amp. Because the low impedance, and the amp output power should be huge. I am not sure the headphone/in-ear will be destroy? I think the power output should be linear, control by the volume. But I am not sure it has the safe point before it reach the headphone maximum power. Or the loud volume I can't endure before it reach the maximum?
You can use the ATH-EW9 with both amps, nothing wrong will happen as long as you keep the perceived volume not too high. These amps have more power than needed to drive your headphones fully, but as long as this extra power is not used, no damage will be done to them.