The compact HP4 can sit on a tabletop or can be screw-mounted to a standard rack tray (not included), where it requires just 1/3 rackspace. And if your needs grow, you can use the line outputs to feed the inputs of a second HP4 or the larger HP60 headphone amplifier. So quit struggling with mediocre headphone amps. Get the HP4 and hear everything loud and clear. You owe it to your music.