Mackie HM-400 4-Channel Headphone Amplifier

If you're after a professional headphone amplifier, then the Mackie HM-400 is an excellent option. It's a 4-channel amp with 3 headphone outputs per channel that's suitable for the studio or rehearsal room, for instance. Each channel is equipped with an aux input with balance control so you can mix your main and aux signals together. Keep an eye on the volume level by means of the LED meters on each channel plus the main. For ultimate usability, you can even mount this one-unit device in a 19-inch rack!