behzad, try read this useful article "Why Are My Beautiful Scans
Terrible When Offset Printed" about RGB-CMYK convert and blacK color generation. It's not give ready solution to you, but can help understand cmyk.

Try generate CMYK from your RGB-bitmap in Photoshop with "Heavy Black Generation" - that can make your color maximum "burn" as cmyk can. Load your RGB bitmap and play with settings: Photoshop -> Edit -> Convert to Profile -> Custom CMYK -> ...