| Most all of the pieces of setup can have some impact on volume. Sound post fit and placement. Type of tailgut, bridge fit, etc. I've never gathered that one is more important than another. Our resident pros may have a better sense of that than I. And it is almost always going to be compromise. For example, you can set the post right on the G foot and get a focused, mid-rangy, seemingly "loud" sound, but you might give up bottom end and tone color in exchange.
DB volume is a rather deceptive concept anyway. The player is in the worst position of all to judge how the bass sounds.
IMO, the most important thing is whether or not the bass is set up to allow the player to get the most volume out of it.
Is the fb planed and shaped to allow the string to move?
Is the string height high enough to give the string room to move?
It's up to the player to move it. High strings aren't a must for high volume. The better your technique, the lower you can set the string and still get a big sound. If you attack the string with precision, you can get in that groove that it moves plenty and doesn't hit anything. If you aren't so precise, you have to run them pretty high to keep from clattering on the fb.
Your best bet is to take it to a luthier and play it for him or her. Talk about what you don't like ( and do like) and listen for suggestions. | 
