The rendering of CMYK formats in PM is not as accurate as it is for RGB (whether sRGB or AdobeRGB or BruceRGB etc) when your monitor is properly calibrated. This has to do with color managing CMYK to an RGB output device (your screen). But you shouldn't worry as long as your printing program (e.g. Photoshop) is doing the right thing when it converts to CMYK, after all, CMYK is for printing and it should be targeted for a specific device, ink set, paper, etc. The ability to proof print is on our long list of features to add, but we recommend you stick with a program like Photoshop that has a long history of dealing with printing and CMYK conversion.
IOW I wouldn't use a CMYK TIFF as a source file in PM to do a Save As because of this color management issue. The CMYK TIFF file should be created by Photoshop (from the RGB JPEG and with all of the press settings known), and then it should be the end-of-the-line for that file. Don't use that CMYK TIFF in PM to save an RGB JPEG for example. Consider PM's view of CMYK files as "an approximation", not the final word on how it will look.
Its not clear exactly what your workflow is so excuse me if I made some silly assumptions...
HTH.
--dennis
