Thanks for the additional information. I apologize for not responding sooner, I've been tied up with workshops over the past two weeks and not on email as much as normal.
How often have you been agitating the ink carts since they were installed?
How often has the printer been used vs. how long has it sat unused?
What are the temperature and humidity levels in your printing environment?
When did you start having problems with these three channels not fully printing?
What happened before the channels stopped fully printing well- had the printer sat for a while, were carts refilled, etc...?
The refillable carts work very well, but a big difference between the refill carts and Epson carts is that the refill carts draw ink from the bottom, so if not regularly agitated, pigment will settle and thick ink from the bottom will be drawn into the ink lines, causing particle build up in the dampers to occur faster than normal. If this is the case, then dampers can't be cleaned and need to be replaced. The dampers ("Ink Selector Unit") costs about $195 from Compassmicro.com, here: http://compassmicro.com/parts_detail.cfm?ID=6812&form.mfg=Epson&form.printerstyle=Inkjet&form.printername=Stylus%20Pro%204900 (which is a lot less than throwing away the printer and buying a new one). Repair procedures can be found in the Epson field repair guide, which you can get online, one place is www.2manuals.com
Please let me know, thanks~ Dana