If you Google "semen volume increase", you will find much discussion about this on the Internet.
I wouldn't have thought there is really much you can do to increase what is natural for you, and output varies between individuals. I think all you can realistically do is maximise your own output by staying hydrated, but I'd be interested to read what some of the medical professionals here might say about that.
It seems there are plenty of pills out there that claim to increase your volume, but I wouldn't believe a word of their sales blurb as what they say isn't backed up with research. You might as well be buying snake oil. I wouldn't bother.
Sounding? What could that possibly have to do with it? I don't see how you might think it has any bearing.
Anyway, as long as your orgasms are good, does your semen volume really matter all that much?