From your photo, the light source is still too close to the objects, that is why you have a quickly decaying falloff. Your softbox setup is insufficient, either because your softbox itself is small or your flash power is small. Note that a close diffused light still shows properties of a point light, just the shadows are softer.
To entirely avoid shadows, you need a light shed, similar to the one on this link. Note that you can buy the shed itself separately, in different sizes, the largest is ~64 USD. And you set up your flashes the way it is shown, and you are all set.
To avoid shadows, the general theory is to have as many light sources as possible. With continuous light, you can do this with LED lamps, with flash, you can do it with many flashes, or by diffusing the flash. Note that you have to flash away from your objects, on a large diffusor area, e.g. a white umbrella, or just a large white paper, and not the way you seem to do it, flashing through the softbox, directly to the objects. (You could do this with a huge flashbox and a studio strobe, but it seems you do not have the proper equipment for direct flashing.) I was able to do completely shadowless product images with only one flash and a large bent white paper, just reflecting the light from the paper.
So use indirect lighting, with possibly as much diffuse reflection of the light as possible before light reaches the objects, and you will have no shadows.