From what you explain, it sounds like you are experiencing flow issues, and since you reported magenta and yellow, which are always the thickest pigment inks (this is true even with Epson inks, and due to the natural pigments used), I question the dampers and printer's maintenance history. After reviewing your order history, I see you have been using ConeColor K2 inks in your 9600 for several years now. When (if ever) were the dampers last replaced in this 9600? Have you cleaned (or replaced) the capping station, flushing box and/or wiper blade? Have you cleaned the bottom of the print head? On average, how often do you use this printer vs. how long does it sit unused? What is the humidity level in your printing environment? What is the ink level in your refillable cartridges? Are the air vent holes fully open for proper ink flow? How often do you agitate your ink cartridges to maintain in-suspension pigment?
Please let me know so I can help you resolve this issue and get back to happily printing.
Best regards~ Dana