Hi pinkypinky,
Thanks for posting your success (though it was a lot harder to get there than it should have been). The main issue seems to have been this:
we had to discard the driver OSX showed in the list
Which means if you had been using your Mac they way it comes from the factory, then every Apple supplied print driver under the sun is on your hard drive. That's gigabytes of data you're highly unlikely to ever use. I've always found this method to work without fail:
1a) Do an Erase and Install of the OS. Do a custom install and select just one set of print drivers from those available. Since one of the printers I have is an HP 5000N, I selected the HP drivers. All other unchecked.
1b) If you don't want to do an Erase and Install, you can also just go to the /Library/Printers/ folder. Put everything in the trash except for the folders "PPD Plugins" and "PPDs". Open the PPDs folder and trash everything in it.
One way or the other, OS X's basic print engine needs to be installed. If you were to do a custom install and not select any printers at all, then that part of the system is not installed. So you need to choose something.
Once I had finished a fresh install of OS X, I emptied all of the items in the /Library/Printers/hp/Icons/ folder except for those few belonging to the HP 5000N. Same with the /Library/Printers/PPDs/ folder. Tossed everything except the PPD for the 5000N.
2) Now that you have the basic print system installed with no extra data, install the appropriate drivers from the manufacturer. I was able to simply use the disk that came with the 6280 DN, and it worked with no hassle at all. All other printers I added also worked with no issue.
The drivers OS X installs are supplied by the companies who make the printers they're for, so it doesn't make sense when they don't work. My method may seem a bit extreme to some, so I don't recommend it for everyone unless you, a)
Have a complete backup before you remove anything!, and b) don't mind doing it, and have a good idea of what you're manually removing from the hard drive.