  We report on recent upgrades to our general relativistic
radiation-magnetohydrodynamics code, Cosmos++, which expands the two-moment,
$\bf{M}_1$, radiation treatment from grey to multi-frequency transport,
including Doppler and gravitational frequency shifts. The solver accommodates
either photon (Bose-Einstein) or neutrino (Fermi-Dirac) statistical
distribution functions with absorption, emission, and elastic scattering
processes. An implicit scheme is implemented to simultaneously solve the
primitive inversion problem together with the radiation-matter coupling source
terms, providing stability over a broad range of opacities and optical depths
where the interactions terms can be stiff. We discuss our formulations and
numerical methods, and validate our methods against a wide variety of test
problems spanning optically thin to thick regimes in flat, weakly curved, and
strongly curved spacetimes.
