As for the fans issue, there are 9 fans, there are 4 thermal zones. Some of those fans are attached to specific devices.
If you're looking at the side view on apple.com/powermac/design.html
, the bottom thermal zone is for the power supply. That's one fan.
The next thermal zone is where the processors are. There are two fans prominant almost half way between the front of the case and where the processors reside, sitting next to the ram slots on the side laid logic board. There are two more fans at the back of the case where the two fan grills are, so this thermal zone has 4 fans. Each of those fans are wide.
The next thermal zone is for the PCI cards. Because this is a side view, you cannot see depth or dimension. The fans are only at the front, but there are two there, each taking up half the width of the computer.
Then with the top thermal zone we have the same scenario for the drives. Two fans, but you can only see one because it is a side view.
So unless you know what to look for, you can't see a fan for the power supply thermal zone, you only see two fans for the processor thermal zone, only one fan for the pci thermal zone, and only one for the drive thermal zone.
But there are 9 fans, and 7 of them are computer controlled speed dependent upon tempurature.
Which two are not? The two for the back grill. They would probably run at a constant slow speed for minimal noise output. These two fans will keep the airflow of the entire computer moving, wether fast or slow, in the off case another fan fails.
I hope this illuminates this topic, as I've seen a lot of arguement on this.