6 Color Process (Hexachrome) Printing File Set Up Help

I am doing a print job in illustrator for a heavy plastic bag/package. The printer will be using a 6 color process (hexachrome). Should I set up my document color mode as RGB or CMYK? Also, do I just choose colors from CMYK swatches, Pantone Process swatches, or something else? I can't get the information direct from the printer (it's complicated).