Normally a headphone amplifiers has a very low output impedance which gives the amp tight control over the headphone action.
翻一下：一般情况下耳机放大器为了对耳机控制有很低的输出阻抗。
2
The embedded headphone "amp" is probably just a good-enough chip amp.
内置的耳机功放或许只是一片还不错的功放芯片。
3
Additionally, the onboard headphone output makes it an ideal practice amp day or night and the dedicated CD input allows you to hook up a portable CD or MP3 player to practice along with.