When choosing matte photo paper in the print box, the printer uses PHOTO black ink. The ONLY way to get MATTE black in to work is to use one of cannons "fine art" paper selections. I printed test prints on each setting using cannons color profiles each time using matte once and photo rag once. Then used the manufacturers for photo rag and matte photo paper.
When everything was said ad done, the images with their 35mm margin had deep deep blacks and once printed full page using matte photo paper setting, blacks were black but dull as all get out. Try it yourself. I am glad I spent the money on the cartridges to figure this out. People were complaining that the matte photos looked dull.
The engineers at canon (what a PITA they were to get to from the customer service reps) confirmed that the driver ONLY uses matte black ink when choosing a fine art paper drop down in the print box.
PS the only way to get the printer to use the "gray" inks is to tick "Grayscale" in the box before printing, otherwise uses black and other colors to create grays.
Dont take my word for it, try it yourself. take a black image in a small box, print once with matte photo paper and then again with photo rag settings. Use the same paper both times and same color profile. You will see a HUGE diference!
Hope I could help anyone who stumbles upon this in the future.