Actually I'm quite familiar with filling refillable carts but it's always been black or various dilutions of black for a couple of inksets in Epson printers. It's been fairly easy mainly because I use only one syringe, rinsing it thoroughly between carts. Do you use a separate syringe for each color? The Easy-Fill technique looks even easier, if I understand correctly you can buy the ink in disposable plastic sacks that fit into the shell - the shell contains the chip. Might be more expensive per fill however.
Perhaps Jeff will chime in here. To each his own, I guess!