We report a numerically designed highly nonlinear all-glass chalcogenide microstructured optical fiber (MOF) for the efficient generation of light around 6 mu m through degenerate four-wave mixing by considering a continuous wave CO laser of 5-10 W power emitting at 5.6 mu m as the pump. By tuning the pump wavelength, pump power, fiber dispersion and nonlinear properties, a narrow (N)- and/or broad (B)- band mid-IR all-fiber light source could be realized. Parametric amplification of more than 20 dB is achievable for the N-band source at 6.46 mu m with a maximum power conversion efficiency (C-m) similar to 33%, while a amplification similar to 22 +/- 2 dB is achievable for a B-band source over the wavelength range of 5-6.3 mu m with a C-m > 40%.