There is a gain switch on the WA11 itself. It only affects the sound that's coming out from it, not what that's going in.
I suggest that you take a look at what this product is actually. It may help to answer all your questions already.
I understand what the product is. We were taking about two different things. I was wondering if lowering the volume of the input going into the WA11 degraded sound quality. I thought you were calling that gain. Now I understand you were referring to the switch on the WA11.