Maybe you should check your fan curves just one more time, because when I look at them I see this:
And this is waaaaaaay off the manufacturer's specs (which I looked up thanks to your highly detailed Engineering Database notes.) I changed the fan curves in the model (and I changed the fan lids to simple discs, you don't need to model the core), and the results look better. I got about 80 CFM per fan from the top three, and almost no flow from the bottom two. This makes sense to me because those fans are extremely weak, they stall out at 73 Pa of pressure which is almost nothing, I don't think those are the right fans for the job.