Is it a set up problem?

[Ken Smith]

I think that the sound is in the wood. With a string length of 104cm (40.94") you have a small 3/4 sized bass. The pizz boom you talk about might be lacking from the thickness of the wood and just the overall size of the bass. I would assume at this point that the bass is factory made (pictures might help to guess better) and that the wood is fairly thick in both the top and back. Bowing the Evahs which have lower tension but a bigger diameter makes sense as the Spiros have greater tension and might be choking the sound a bit.

I have one bass that is on the smaller side like yours and it too lacks that depth that sounds deep and shakes the floor. It's loud and carries and has a nice boom but the size of the bass prevents itself from sounding like a larger bass that could be deeper sounding. Actually, I have 2 such basses at the moment. Both are fantastic sounding but that deep dark floor shaking boom you are looking for usually comes from a larger sized bass. Both of my basses I speak of are handmade and much older than yours. Still, they can only be what they are and they are just fine sounding like themselves. If I want a deeper bigger 'boom' sounding bass, I just go to a bigger bass. Problem solved.