  We present an extension of the harmonic-space maximum-entropy component
separation method (MEM) for multi-frequency CMB observations that allows one to
perform the separation with more plausible assumptions about the receiver noise
and foreground astrophysical components. Component separation is considered in
the presence of spatially-varying noise variance and spectral properties of the
foreground components. It is shown that, if not taken properly into account,
the presence of spatially-varying foreground spectra, in particular, can
severely reduce the accuracy of the component separation. Nevertheless, by
extending the basic method to accommodate such behaviour and the presence of
anisotropic noise, we find that the accuracy of the component separation can be
improved to a level comparable with previous investigations in which these
effects were not present.
