They seem washed out on-screen. But I think you'll find that a properly prepared image in any color space will do fine on paper.

But it would seem to me that triple-processing you show in that link is a fault in work-flow. I would leave the image in XDP (or whatever you are using) as an RGB. If you must/desire to at least see it as a "gray" image, use the Saturation tool to desaturate it. Export your PDF. The image appears gray, obviously still an RGB image.

Use the Convert Colors to change it. Set the Object Type to "Image." Set the "Conversion Profile" to say a 10% dot gain if going to print digital, perhaps higher if using offset (typical would be 15 to 20% depending upon the press). Click OK.

Now look at the saturation.