I know - "just fit another PSU", but no, I'd rather not, as the computer is stuffed, and the current PSU is capable of sustaining the load.

There's a couple of problems I see here. First, you're assuming the existing PSU is capable of sustaining the load. But you just got done telling us how your diagnostics determined that it can't, in fact, handle the load. Listen to what you're saying.

The other, larger problem I see is this: You're trying to stuff ten hard disks into a PC's casing. That'll work for about three months before the combined heat from the drives begins to cause them to break down, one at a time. Drives configured in stacked arrays like that need lots of ventilation. Dedicated fans directly blowing on the drives are essential in that kind of a system.

I've had thermal failure troubles when stacking as few as three hard disks, and you're doing ten.

I'm pretty sure they make external cases specifically designed for the sort of thing you're trying to do. Research it. If you don't, the failures and maintenance will kill you in the long run.

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Tony Fabris