I spend my days trying to match RGB colors in CMYK... it's not easy and some colors you'll never hit. While I think this should be a spot job if you want to try CMYK you may need to dumb it down a bit. On the yellow go 100%. On the blues... go 100% Cyan then gradually add Magenta to your other blues. On the next darker blue add 5-7%M, next 10-13%, etc.
You can also choke the magenta a pixel to make registration a bit easier on the press. I would also rip out all of the black.
We have been doing it for years and have custom color profiles and values for all of colors. This for heat transfers not directly on garments but the concept is the same.
