We numerically simulate and optimize a high-power fiber Raman amplifier cladding pumped by spectrally combined diode lasers at wavelengths from ∼0.9 to ∼1  μm in the continuous-wave regime. This amplified a signal at the first-Stokes wavelength of 1024 nm. We found that it was possible to add pumps over an increasingly wide wavelength span up to ∼90  nm, while still maintaining an incremental conversion efficiency higher than 60%, even though the Raman linewidth is only ∼15  nm. We investigated the dependence on the power of individual diode lasers and on the wavelength spacing and found that the total conversion efficiency reaches ∼70  %   with realistic pump sources based on state-of-the-art diode lasers. We believe this study shows the potential for high-power fiber Raman lasers pumped by spectrally combined multiwavelength diode and fiber laser sources.