I recently noticed that if you disable catver.ini, in options, you can use any custom category ini, supported by MAME emu, as the QMC2 category file. This includes (but is not limited to) everything in the EXTRAs\folders directory, except nplayers.ini, which does not work in MAME, as it is in the catver format, and should be replaced by Multiplayer.ini (also from the nplayers site - the mameUI download).