Box 1 and Box 2 are identical except:
16GB USB stick for Ubuntu (Box1)
SATA HDD for Win 8.1 (Box2) - GPUs are undervolted using MSI Afterburner.

Motherboard   Gigabyte 990FXA-UD3
CPU    AMD Sempron 145
Memory   8 GB 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800)
GPU    Radeon R9 290 x 6 (mixed Brands MSI and Asus)
5 x Powered Risers, 6th GPU is plugged into Mobo directly.

3 Power Supplies:
2 x Rosewill LIGHTNING-800 800W
1 x EVGA NEX 750G