>That was one of the first things we tried and, logically, seems like it ought to be the answer, but it wasn't. It probably was one of the attempts that made the front panel lights behave correctly (i.e., stay on the draft setting instead of kicking over to NLQ), but the actual print quality comes out the same--near letter quality and slow....

What about fonts and font sizes? Special fonts and sizes will require multiple print head passes. You would not have this problem in your Notepad[?] test.