I really feel that the humidity issue may not have as much to do in preventing clogs, as living in Arkansas with 100% humidity most of the year, I have had plenty of clogging issues with my 9900, just many users seem to have. I don't use a humidifier here as on average expect winter (3 months) the humidity will be 80 to 100% on average. My printer is now close to 4 years old and is used daily.
Sure I run an AC in the house, but they only do so much and for sure are not pulling 100% of the humidity out of the house. I figure I am easily in the 45 to 55% humidity range here.
In 4 years, my main issue has always been the totally dropping of one entire channel, most times after a couple of prints, where everything was fine in the previous prints. This always seems to be more prevalent after a PK to MK change. My feelings are this is more of an electrical issue, something going on in the ink delivery system, maybe in the channels leading to the head or possibly the dampers.
John, glad to see D One got you back online.
Paul