Over the past few months I've converted two 9890s. One had a dead yellow channel. It's now loaded with gloss & matte K6 warm black. I loved that one so much that I went looking for another printer with a dead channel for few $$s to use for a gloss version of the new Pro set. Love the look of gloss prints on the first printer but two pass printing on rolls is a pain and waste of paper. I ended up finding locally a perfectly working 9890 at a very attractive price. I've loaded it with the the full Pro set.
I used Piezoflush to purge both printers before loading ink. The process is easy though tedious. Loads of docs and help here. Since being loaded with Piezography inks both printer very, very rarely show less than perfect nozzle checks (except for the dead yellow in the first). I own a commercial studio but these printers are primarily for my personal work. In other words they're not used all that often. Still no reliability problems with the ink/heads.
I'm still very much new to Piezography and trying to learn its gazillions of intricacies, but this is far and away the most exciting photographic process I've encountered in years.