Biostar TB85 - 6th RX480 Crashes Windows on Startup

I need some guidance on a new rig I am working on. As soon as 6th GPU is installed, Windows won't boot and goes BSOD. 5x GPUs runs smoothly without any issue.



Hardware
Biostar TB85 Motherboard.
Sapphire RX 480 8GB Nitro+ x 6 units.
Corsair AXi 1500W PSU.
GPU Bios Un-mod.
All GPU's riser runs on 2 connection per molex from PSU (PSU has 3x rails of molex connector).
Motherboard's molex connection are powered with 2 separate SATA to molex rails from PSU.
Bios PCIE all sets to "Gen 1".


What I Have Tried
Swap "confirmed" working GPUs & risers (I have extra GPUs and riser).
Run only 5 GPUs but plug 5th GPU to PCI-E 6th Port.
Remove molex additional power to motherboard.
Swap with another Coolermaster V1200w PSU.
Switched GPU to silent bios.
Run with all GPU modded bios bootstrapping 1625 memory timing (Bios signature patched).

I suspect power but since AXi has sufficient juice so I suspect bios settings or something I messed up.
It is driving me nuts...please help. I will buy coffee/beer/wine and sandwiches.