These names match those offered for download at http://fms.komkon.org/fMSX/ (albeit in lowercase), and the emulator has been tested against those images.
You may also provide one or more of:
msx-japanese.rom
msx-european.com
msx-american.rom
If one of these files exists, it will be used as the BIOS for machines of that region. If the file does not exist, the emulator will load msx.rom and alter its region identification bytes appropriately.