The motherboards in question are the MSI Z170 KRAIT GAMING and the MSI Z170A KRAIT GAMING, I cannot find any differences between the two boards other than the A in the latter board's name.
Here are the newegg links to each of their product pages...
MSI Z170 KRAIT GAMING- http://www.newegg.com/Product/Product.aspx?Item=N82E16813130879&cm_re=msi_z170-_-13-130-879-_-Product
MSI Z170A KRAIT GAMING- http://www.newegg.com/Product/Product.aspx?Item=N82E16813130868&cm_re=MSI_z170-_-13-130-868-_-Product
Here are the newegg links to each of their product pages...
MSI Z170 KRAIT GAMING- http://www.newegg.com/Product/Product.aspx?Item=N82E16813130879&cm_re=msi_z170-_-13-130-879-_-Product
MSI Z170A KRAIT GAMING- http://www.newegg.com/Product/Product.aspx?Item=N82E16813130868&cm_re=MSI_z170-_-13-130-868-_-Product