So I got my awaited AsRock H110 Pro BTC+ motherboard and finally managed to run 11 GPUs on Ubuntu 16.04. Here's the setup:
AsRock H110 Pro BTC+
Intel Celeron G3930
Corsair Vengeance DDR4 2166 MHz 8GB (4GB*2)
KingDian 16 GB SSD (around $15, best for the price)
9x Sapphire RX 480 8GB
2x Sapphire RX 580 4GB
2x Sapphire RX 470 8GB
3x 850W Thermaltake Toughpower RGB PSU
Since the motherboard is built for mining, I assume no BIOS mod is required. I, however, did change PCIe generation from Auto to Gen1 as this tweak helped me previously with other motherboards. I didn't keep track of my system/BIOS changes and don't know if that change helped. In any case, If 13 cards are installed, an error message is expected at system startup about unfeasibility of running GUI (X-server). Then I thought what about trying miner from text-only-mode and it worked, at least to some extent.
First, install required AMD driver and configure miner program with one GPU in GUI mode. Once the miner runs one GPU in GUI, power off the PC, connect the rest of the GPUs to motherboard (with risers and PSU cord). Turn on; when the error message pops up, enter TTY mode by hitting Ctrl + Alt + F1. Supply PC's login username and password. Now run the miner program from Ubuntu terminal. I will post update if I find something useful.
Of the 13 cards installed, 11 are recognized and mining Ethereum at ~245 MH/s and Siacoin at ~7300 MH/s using Claymore's Dual miner. Instead of doing anything fancy I built an open frame with aluminium bars that cost me only $20.
Miscounted GPUs :P 12 here. I used plastic standoffs on a vinyl board so that the motherboard is positioned securely.
Plastic standoffs on vinyl for motherboard
The PCIe slots on H110 are precariously closely placed. Risers' PCIe ends might cause short circuit. So I secure the ends by wrapping tape around them. I used SATA PSU sync to turn on additional PSU.