First off just because an amp can produce so much power does not mean it will always put that out. You could run your headphones on a 1000watt amp and still be fine if you set the gain to a safe level. The extra power is just headroom. To get an idea of what power levels you need take a look at the specks of your headphones. Most important to amp specks are sensitivity and impedance. For the most part almost any audio amp will have plenty of power to drive headphones.
Also do you want to drive several headphones at once? If so you will need to use gainged potentiometers that can handle the power needed. For the muting use switching jacks that trigger a mute.
Or you could just get a headphone distribution amp.