Wave vs Master volume control issue

I have some logitech speakers that up until a few days ago had been running through analog. I am also running these speakers to my tv's receiver through digital coax. I recently got a splitter for the digital coax and now have my computer speakers also connected via coax and now sound much much better. However, apparently that volume control run by the pc is based solely on the wave line out and changing the master line out has absolutely no affect on my speaker volume. The reason why this is problematic is that my keyboard's volume knob changes the Master volume level but not the wave, so my only choice for volume control is through the speaker's console, which is harder to access and not as incremental.

So my question is can anyone think of a way to either have my keyboard control the wave line or have the wave line be affected by the master volume? Or any other solution to this problem? The keyboard is a really old Dell that doesn't have any drivers or anything. Another solution would be a new keyboard with that sort of flexibility if you know of anything.

Thanks!