The problem is that EarStudio doesn't publish power outputs - just voltage. They published the peak RMS voltage at 2.2V (balanced). FiiO's specs list the K3 balanced output at 7.39 Vp-p = 2.6V RMS. So on paper the K3 provides slightly more voltage. This doesn't really say which is more powerful - to really test, you'd need to put both amps under the same load and measure.