Create a DecalData datablock with the file as the image you want downloaded. DTS files should automatically download, and there's no way to turn off sound downloading since the buttons are broken.
For your server specifically, you should just use the default CI images and weapon models, as I said when I joined (not the one in the new folder of the modified weapon which are just copies), since the people who have the normal weapons won't have to download anything and will see the images, and the people who don't will download the models into the correct folder (for e.g. other servers without your weapons) and not see CI's like in servers with the normal weapons, unless you force-download the original image files.