Sounds like you've correctly tried the all the standard things. To keep it simple, you may
be looking at a head replacement, pump replacement, and possibly a replacement of the ink lines between the carts and the head. IMHO, any of those would be a waste of money compared to buying a whole new printer on one of the many wide format printer end-of-year sales specials going on right now. For instance you can "trade in" your 9880 for $1000 on a new Canon 8400, which also has a $1000 rebate (in the US). And Epson has some deals, too. Printer restorations are much less fun than actually using them.
Was the printer sitting outside in a surplus yard, or was it stored in a hot location like a shipping container? If so the ink in some of the lines or printing head may be petrified. You can buy special carts full of inkjet embalming fluid to clean them out in that case, although there are reports of mixed success in doing so.
And even when you get that printer up and running, you are still going to have to deal with all too regular nozzle clogs. I had a love/hate thing going with a 9880 for a few years, we finally got divorced. But oh, could she ever print when she was in the mood!