Archived - Apple TV (1st generation): Apple Remote can control music volume
Plus and minus on Apple Remote can control volume of music on Apple TV.
The buttons labeled "+" and "-" on the Apple Remote are used to navigate the Apple TV interface and are referred to as Menu up/scroll and Menu down/scroll. Starting with Apple TV software 2.3, these buttons can also control the volume when playing music.
To enable this capability, choose Settings > Audio & Video > Music Volume Control. To change the volume when playing videos, use the remote for the audio device (for example, the TV or A/V receiver) to which Apple TV is connected.