most panoramic games use a cube so start here:
https://sourceforge.net/p/pipmak/wiki/Making_Cubic_Panoramas/
there was a tool for FPSC to make skyboxes called CloSk_Skybox Creator_V1.0.0, it comes with the free download of the engine
pano2vr can convert spherical images to cubic or cube cross
once you have a textured cube use the sky_basic.fx
the issue might be seams