I have 3 audio tracks, 2 are audio inputs on my Focusrite interface and the 3rd is USB audio input from a Virus Snow.

Track gain on the Virus track works and adjusts the incoming volume but track gain on the other 2 tracks has no effect at all.

I was sending all the tracks to buses and using gain on the bus but thought this might be a waste of resources, why not just do it at the track level?...until I had this issue.

Volume fader has the expected effect just not the track gain.

Any ideas why track gain is only working on the Virus track?

Hey Shambler.
 
Track gain on the inputs from your audio interface is controlled by its own control software panel/utility (or physical gain knobs if it has any). 

As Bruce said, If your talking about setting recording levels, that has to be done at your interface, Sonars track controls only affect the playback not the recording. 
And the gain control most certainly works on playback. 

Excellent thanks guys I've learnt something :)
 
The signal coming into the interface isn't too hot so since I use CA-2A on every track I think I'll just adjust the gain on that instead of constantly adjusting the input gain on the interface.