Changing volume on external speakers

[mad-jamie16]

Hi guys, iv'e just got a pair of speakers for my imac and there awesome but the speakers were used and didn't come with the remote. i usually change volume on my imac with the keyboard but it doesn't allow me to with external speakers. does anyone know a way of changing this so i can change the volume on my keyboard until i get a new remote for the speakers?
Cheers, Jamie.

 

[JediMeister]

How are these speakers connected to the Mac? USB, audio input 3.5mm jack, bluetooth? Just trying to get more info to help with replies.

 

[mad-jamie16]

How are these speakers connected to the Mac? USB, audio input 3.5mm jack, bluetooth? Just trying to get more info to help with replies.

There connected via optical (mini toslink to toslink). the thing is, i can change the volume using the keyboard in windows bootcamp so im guessing its something to do with os x?