FlyingHelmet :
are there no 260s or 250Xs that are sufficient?
Oh du, i'm sorry i forgot to check the other video cards, yes the r7 250X supports 6 displays with a MST hub.
http://www.amd.com/en-us/products/graphics/desktop/r7#
BTW...If you have a intel i3 or i5, you can easily get away with a Geforce GT 730 or R7 240, because you can plug three of the 6 displays into your HD 4600 and the other three into the GPU.