How to do base-band simulation of coherent detection of M-ary orthogonal signals?
Since the answer was given by vaz in the comments I figured I would just post it as an actual answer...

To perform coherent detection for M-ary orthogonal signals in a complex base-band simulation simply take the real part of each matched filter (correlator) output and select the symbol with the largest value.

Also, don't make my mistake and use the absolute value of the real part.  I made those changes and verified against the theoretical coherent equations MATLAB uses.