as alternative of the mining MB Asrock pro BTC , i have made a list of other alternative of lower price 6 gpu and 7 gpu motherboards can used be in mining at this link
https://cryptocurrencyupdates.blogspot.com/2017/04/list-of-6-7-gpu-motherboards.html
https://cryptocurrencyupdates.blogspot.com/2017/04/list-of-6-7-gpu-motherboards.html