I'm sorry for the late reply, but you should use Qt 4.7 from the git repositories. All the necessary changes are in there and it builds cleanly with sezero's toolchain, out of the box.

You will need perl in your path.
Just run "configure -phonon -qt-style-windowsxp -qt-style-windowsvista"
These options are needed because Qt's configure does not search the right paths for the necessary header file and thus it does not enable the features, but they do work with mingw-w64.