In this letter, we propose the extension of a previously presented analytical model for the estimation of the signal-to-noise ratio (SNR) at the output of an adaptive equalizer in coherent optical transmission systems when transmission is modeled as a generic 2x2 matrix transfer functions, to be applied to polarization multiplexed communications based on advanced modulation formats (PM-QAM). We present the model and then we extensively test its accuracy on an possible application environment. Our findings show a remarkable agreement, with maximum SNR discrepancies of about 0.5 $dB$ between time-domain simulations and analytical results.