If you wanted more inks (when isn't more better?) you could get additional printers of the same model and convert the cartridges to other colors and/or make lighter variations of the supplied inks. Each additional printer increases gamut and smooth out tones. Here’s an outline of what you’ll need:
Get a JBOI profiler (Just a Bunch of Inks plus the spectrometer and associated software, you can Google for JBOI profile suppliers) that builds up a profile from any old set of inks across multiple platforms. The JBOI profile is integrated with the Sequential RIP (SRIP), which seamlessly manages sequential incremental printing across multiple printers. Make sure all printers are in registration (turn on the auto registration check feature in the SRIP application). Feed the same paper through all the printers. After feeding the print through 4 separate printers, all Canon printers in this example, (for the record, I am not a Canon dealer), you'd have laid down 48 inks for a print of stunning results.