I've been using rgb 000 for my black. Does it actually get converted to cmyk when printing? What does it get converted to? I'm not sure how it works but the black I have is not completely black. It's a bit shiny on the fabric.
What happens to any color during the print process depends on the process. By that I mean postscript or non-postscript. Non-postscript uses the GDI, (graphic device interface) renders RGB000 to a dense black build. Unfortunately the same process renders C0 M0 Y0 K100 to a dark gray.