The two-stage model sounds a lot like the "Hires fix" checkbox in the Automatic1111 interface. If you enable that, it will generate an image, and then generate

The two-stage model sounds a lot like the "Hires fix" checkbox in the Automatic1111 interface. If you enable that, it will generate an image, and then generate a scaled up image based on the first image. You can do the same thing yourself by sending an image to the "Image to Image" tab and then upscaling. If you do it that way, you also have the option of swapping the image model or adding LoRAs. Presumably the two parts of the SDXL model are complimentary: a first pass that's an expert on overall composition, and a second pass that's an expert on details.