To Boldly Go Where....

Very nice model, I agree. I think the background is a picture and if so, the Bryce stars won't show throgh it, except if you make the background partly transparent. There are several ways to get the stars right. You can use a picture or a separate render of the starfield and put it in front of your background. The starfield must have the black transparent. You coukd also render an object mask and combine the star background with the main render using the mask. A more elaborate way I sometimes use is to render the six sides of a cube with the background only several times under different lighting conditions, then transform each brightness series to spherical panoramas and create an HDRI from this. Then I transform it to a light probe for Bryce IBL. I usually use a tone-mapped version in the spherical projection and map it onto a huge sphere. The scene is set in this sphere. The HDRI shines through the sphere and lights the objects while the background looks much better than if the HDRI was rendered as background.

You're right, awesome model. To make stars in Bryce I set it to custom field, intensity to 50%, amount to 15000. And if it does not mess up the rest of the image, increasing the field of view makes the stars and nebulas look very cool.