The voltage regulator on a V006/008 riser is there to stabilize the line and prevent spikes, not generate 3.3V. Why would the traces of the USB connector where the 3.3V is passed from the motherboard on the V006/008 risers be connected to the pins leading to the PCI-E slot on the riser if the riser created it's own 3.3V?

https://en.wikipedia.org/wiki/PCI_Express

Powering the riser with a different PSU as the motherboard causes the 12V line to come from one power source and the 3.3V line and the grounds on the riser x16 PCI-E slot to come from mixed power sources, which is the problem. Sorry, but anyone that says it's safe to power four risers off of one molex strand, clearly doesn't know what they are talking about when it comes to mining.