The baryon-symmetric domain cosmology (BSDC) of Steckeret al. (1971) have explained the diffuse γ-ray background. However, evidence has shown that active galactic nuclei (AGNs) are likely contributors to the diffuse γ-ray background, so there are some problems with the original formulations. We have reviewed the original formulations and have modified the expressions for the matter temperature and the redshifts at which the cosmic radiation from the BSDC becomes significantly absorbed. In this way, we show that the cosmic radiation from the BSDC agrees remarkably with the cosmic X-ray background from ∼1 keV to ∼100 keV. We have also shown that AGNs contribute significantly to the cosmic background beyond ∼100 keV. Therefore, we have arrived at a consistent model in which the BSDC model and AGN model together can explain the cosmic background from ∼1 keV to ∼1 MeV.