You need to use your Stable Diffusion generated background environment to also generate spherical environment illumination maps so you can do image based lighti

You need to use your Stable Diffusion generated background environment to also generate spherical environment illumination maps so you can do image based lighting. That enables the 3D model(s) to correctly match any environment imaginable by projection mapping the environment onto the model; after which the model's materials define if that mapping is reflected, mixed with the underlying surface color, ignored, or some combination percentage. It's how integrated CGI is done in film VFX.