Digital BW, The Print

This might be a basic question, but I couldn't seem to find the 
answer in the archives. I have some grayscale digital images. Is it 
best to give it to the lab saved as grayscale, RGB or CMYK? They 
will be printed using the Noritsu 3002 Lightjet Printer if that 
makes a difference. My natural inclination is to save them as 
grayscale. But I thought I read somewhere it's better to save as 
RGB. Is this correct? Thank you!

John Hartung
www.theartfest.com