Dan,
The media profile should take care of which black ink is used. Did you check in the MCT (Media Configuration Tool) software for that particular media profile? I don't have a Canon printer, but I know that you can see all the details of a certain media profile in the MCT.
Also when you got the am1x file, did you update the printer and your computer with it? That is a function that is part of the MCT. If you have done that, you can e.g. see the Media Profile on the screen of your printer.
And I would give Lexjet a call for sure.
Good luck!
Cheers,
Remko