Volume control with USB Audio device

Hello all.

I have just purchased a cheap USB audio device to connect my HiFi to my laptop with only one, neat USB lead and a USB hub - meaning I no longer need several USB wires and an audio cable across my desk.

This works fine, but I have just noticed that the volume control in OS X has no effect on the output now, only Mute or On. The volume within iTunes works fine, but not the OS X one.

Any way I can avoid having to use the volume on the hifi when using the USB Audio device?

Many thanks.