You should post this on the audio section. We have a few audio aficionados that I'm sure can answer your question no problem. But what model stereo is it and what is the configuration of your total setup? amplifier, speakers, subwoofers...

I find very odd that that the stereo would not control the volume of the subs. I find it even more odd that an amplifier would control it instead... Because an amplifier does exactly what the name denotes. It amplifies a signal coming in.

So let's say an amp has a gain of 10 dB (decibels). All that means is that it amplifies the incoming signal by 10 dB. So if the incoming signal is at 2 dB of power then the output of the amp is at 12 dB. Change the input signal to 4 dB and now the output is at 14 dB, and so on and so on. As you can see, you have to VARY the incoming signal going into the amplifier, and you do that with the volume control. And that is what confuses me.

Off topic- audio signals are measured in Decibels and they are a logarithmic function, in other words not linear. With that said, every 3 dB the power doubles. So if you have a signal of 2 dB and increase it to 5 dB (+3 dB), the power is twice as much now. Increase it by another 3 dB (to 8 dB) and the power doubles again. Keep in mind that it is twice as much as 5 dB or 4 times the power of 2 dB. Another way to put it into perspective: Lets say you have an exhaust that measures at 100 dB and your friend's measures at 103 dB. That means your buddy exhaust is actually twice as loud as yours.

 

 

I'll continue over there so more people can chime in.