Seven months later…
The Win32 build isn’t nearly as robust as the *nix build (as usual).
The *nix build uses mt-daapd-ssc.sh as an easily modifiable shell script to launch command-line tools to do file converting. The Win32 build sacrifices configurability for compatibility — all the transcoding is pre-compiled, which means you’ll have to set-up a build environment, add mpc support to the transcoding script, and compile it.
And at that point, it’d be faster to resize your partition, install your favorite distro, and configure mt-daapd-ssc.sh to include mpc support.