Attached a mingw32 version of dosbox-x (built from 7/19/14 git code; same version as the win32 release built by VS2008). This should mount multiple CD images; however, many lines of code were changed to port to the mingw/gcc environment. This may help isolate the cause of the multiple image mount issue.
Disabled d3d and fluidsynth to compile, although these should have no effect on the mounting of images. Also, added a block of unverified lines to menu.h to recognize the variable "_MAX_DRIVE":
# include "windows.h"
# include "Shellapi.h"
# include "shell.h"
# include "SDL_syswm.h"
Removed dependency of dos_files.cpp on dos_network2 and removed a block of code in sdl_main (?) to avoid errors generated by the newer C++ standard (also removed this parameter from configure).
The attached is only for verifying that the issue is minor and probably related to the build process or a missing header file (although this should produce an error). I'll remove the attached test binary within a day.
Edit: binary removed.