The lightbox is killing your chance at capturing luster. You cannot capture cartwheel luster when using fully diffused ambient (all surrounding) light sources. Diffused light sources will also wash out colors/toning, as is the case on your lovely toned 1915 George V.
Lights need to be at a high angle and well above the coin. If you are going to diffuse your light sources a little bit, do so at the lamp source itself. By that I mean, diffuse each of the lamps with a sheet of paper or cloth, so that they are still reflecting off of your coin as two separate point sources of light. When one uses a diffusion mechanism around the coin (e.g., a light box or milk jug) instead of at the lights themselves, light no longer reflects off of the coin from multiple point sources. The surfaces of the coin will look flat and a bit lifeless, and luster will not show much as the few photons that happen to reflect up into your camera's detector are not enough to create the banded appearance of luster.
As example, Heritage Auctions uses a method to photograph coins in their auctions that diffuses the light at the coin, not at the point light sources. Here is a Heritage Auctions image of a coin I own.
I use diffusion at the point source of the lights, and place the lights very high and close to my camera and lens. This method brings out color, luster, and the life of a coin. Below are my images of the same coin (yes, even through the plastic).