7. What is the function of the M15's Over-ear headphone mode?

The default power mode of the M15 is for earphones. If you're using over-ear headphones with high impedance, you can turn on the Over-ear headphone mode to get higher output power, which can be up to 800mW for balanced output at 32Ω , and up to 275mW at 300Ω. This means that the M15 can drive most of the over-ear headphones in the market with ease. However, note that the high output power is not suitable for high-sensitivity headphones, so you should avoid using them in Over-ear headphone mode.