I have no experience with digital negatives, but you may find that many of the after market pigment inks have a smaller dot gain than the Epson inks, so you might see some banding. Also some of the printers do not have a strong enough motor driving the heads to haul the tubing, which again can show up as banding.
I have not played with any CIS for the new Epson dye ink printers, so I don't know if that ink is worthwhile, or how the printers deal with the CIS. I do have an Ink Republic CIS on my CX6600 at work, and it does a credible job with Image Specialists pigment inks installed. I've printed reams of paper, but mostly manuals for things, not photos. It does do a decent job on the few photos that I've printed even though it is only a 4 color printer (using mostly only 3 colors for photos).
Sorry I can't help with your question more than this.