In a "proofing" environment, you typically build your color management to emulate the final output device. This usually means an offset printing press. Your print driver's job is to emulate that device using it's own internal capabilities. In your case, color laser cartridges. As you build files, you sort of establish a defacto workflow that fits perhaps as much as 80% of the default output devices out there. Nowadays that means a digital RIP connected to a digital press or a conventional press using a direct-to-plate workflow.
So, just briefly, I think your mis-interpretation of color management is building your files to the printer's .icm, which usually is applied in the final step in the process = proofing. In short, if your job is intended to be printed to match an offset press, then you use the press profile in your file(s). Of course, a lot of things can go awry along the way. Color management tries to limit the number of things and, in the process, establish some type of standardization ( consistency ). I briefly took a look at the Oki 9650 ( 9600 is discontinued, nice huh? ) which comes standard with Windows Postscript emulation. This is a good thing, along with PCL5, which are good drivers. That said, Postscript emulators usually do not provide a solid proofing solution and, historically, laser printers are not very good proffers either.
You don't need any more confusion, so I'm going to back off a little on your workstation. I also noticed that the 9600 is considered a good signage printer, which probably means that it is limited to 4 cartridges = CMYK. Add to that the printers' limited ability to render a decent gamut, and the problems start to become evident. In short ( again ), a laser CMYK printer will have difficulty matching color and in some cases, will never render some specific colors. Add to that your monitor which displays color way outside the CMYK gamut spectrum.
Your workflow could easily be color managed, but you have to be realistic with your expectations given the limitation of your existing workstation. At a minimum, you should ( if you haven't already ) invest in a good spectrometer ( look into x-Rite ) and a good profiling system ( Monaco Proof ), along with hardware that can calibrate your monitor. In addition to that, see if there are any 3rd party true Postcript Level 3 RIP's for that 9600 ( Colorburst, Wasatch, etc. ).
Adobe.com has some white papers on color management for designers. They get into proper application settings, including Black Point Compensation; Rendering Intents; and profiles. Again, using color settings in Bridge is not a bad idea. It would be nice to see what yours are. I tend to set individual application color settings because the Rendering Intent I use in Illustrator is not the same I use in Photoshop. You will find much more consistency once you've calibrated correctly your hardware. I would not rely on your monitor, no matter how good it is, to softproof your work. Big mistake. The ideal solution is to establish a reliable proofing output and base all of your color decisions on that instead of the monitor which only leads to frustration.
I also noticed in the 9650 specifications, that OSX is 10.2.4 or higher is listed. What may have happened is the OS is incompatable with your drivers and, therefore, may be a problem with OS communicating with your printer. Snow Leopard may have drivers for the 9600, have you looked? I'm concerned about the drivers and the OS. Any recent updates for your printer? I suspect Oki has abandoned that and now supports the replacement printer...the 9650.
Were you able to get your problem resolved, Andrew? The only thing I can suggest is to check your different drivers and make sure everything is working okay. Please keep us posted and let us know how things pan out and what the problem was.
You might want to try using an RGB workflow.
Try this simple experiment: instead of placing a CMYK scan in InDesign place an RGB photoshop file (.psd) and export the PDF with your printer's profile.
What is effectively happening is the CMYK conversion is happening during the InDesign > PDF export. InDesign may not be converting placed CMYK files with satisfactory results.
Hope this helps.