"I simply do not believe their claim that they can get the Epson printers to print at greater than 1140 dpi - or if they can, their technical service department has never bothered to answer any of my queries on this."
That bit is pretty simple - the Epson printers print at 720 dpi. 1440 dpi = 2 passes; 2160 dpi (Peizo. driver) = 3 passes; 2880 = 4 passes. Thats why the registration and transport system is important and the better bilt printers are better.