Well...
If you print the image as a single hit frontlit-profiled image, and then triple hit the black, I don't think you're going to be all that happy with the final result. The image of the Captain is going to wind up looking pretty washed out when backlit, and surrounded by an actual opaque black background, that's liable to look pretty bad. Plus if I'm following you, and what you're trying to do is hit three times with the black channel only... I guess you could, but that's not how it's typically done.
Opacity and rich black in large format are made with under colors, not by adding more black.
Best thing to do of course is to run that with an actual backlit profile, but other than that, what I'd do if I was you was to run the file as RGB -- sRGB would be easiest and no doubt fine -- make sure the black is R0, G0, B0 in your file, then you can look in Job Editor and see what the actual values are you're printing in the black area. Whatever they are, they'll be the ink limit as set in whatever profile you're using.
Then double-strike the entire thing.
(Edited to add: Of course if you have white ink in that Oce, the very best way to do that would be color-white-color. No changes needed at all. You can create the white flood right in Onyx.)