I have a Mediastreet sytem on my 2200 and 7600 as well. The results are excellent and the print quality equal to epson inks in my opinion. One issue with this printer is the yellow cart/head. It clogs frequently and I have had to it once. The mediastreet folks have been responsive and helpful. They are aware of the problem and thnk it is design problem involving the position of this cart--they pont point out it has been moved in more recent printers. Other than this irritance, I have been very happy with the quality and savings.
I had the same issue with Yellow on my MediaStreet Niagara on a 1280, G Chrome pigment inks. I then raised the ink bottles/stand by putting it on 50 sheet paper box and the problem seems to have gone away.
Maybe you want to get some large diameter washers from a hardware store and try shimming your yellow ink bottle. I just now remember reading on the web site of some other CIS supplier that Yellow pigment ink was problematic because it was thicker.