there is a provision for a fan for the PSU, the CPU cooler fan, and a couple of case cooling fans. you dont really need to put them in any specific order, all fans are 12 V, but the BIOS and software might have been written assuming certain order on usage of these headers.
that is why the manual says to put the power fan in specific FAN2 header.
girish
<font color=red>No system is fool-proof. Fools are Ingenious!</font color=red>