I've owned a 4880 for a few years (read: not an expert), and have been following this topic here in the forums. My experience agrees with what I've read as the three most commonly accepted reasons for "clogs" in Epson wide format printers:
1) New printers and sometimes new ink cartridges make bubbles in the lines that, when they reach the head, cause the whole channel to go out. When my printer was new, I could actually see the bubbles in the line. I don't know if the 4900 is built differently to avoid this, but if not your replacement printer will experience it too. I don't know a way around this.
2) Humidity. Winter in most places means dry air. These epson printers seem to fair much better in moderate humidity (not too low and not too high). After going away for Christmas, and leaving my printer unused for over a month (oh, and I live in the desert that is Utah) I was experiencing what you describe - most channels almost entirely clogged. After struggling with it for two days and getting very worried, I remembered that I should have had my humidifier on. After turning that on for a day, I came back to it and the nozzles all cleared up by the second cleaning! (not power cleans)!
3) Cleanliness. Avoiding dust always seems like a good idea for these touchy devices.
When I cut the previous print from the roll, the newly created edge on the roll should be wiped to remove any tiny paper bits. It seems to make a difference for me - or maybe it's just a superstition that I've built up.
Hope this was helpful.
Good luck with your new printer!