9 days is easily doable in my experience. I've just done a test pack for my trip this summer with my son, which requires 5 days, 4 nights, x 2 people, and it fits no problem.
If you're not fussy about food, you can do even better. Instant potato with olive oil added (carry the olive oil in a platypus not a hard bottle!) takes very little space and is very calorie dense. Spaghetti similarly is very space-efficient. Rice and M&Ms can both be poured in at the end (a small sheet of card with rice sized holes can be used to separate them out again).
My record is 10kg of food in a bearvault, and this included stuff like snickers bars, not just dried stuff in bags. Repackaging is an important part of the process - e.g. potato flakes need to be taken out of paper/foil packets and put into ziplocs.
