Sense the DEV of afterburner said he won't support anything over 8GPUs and calls mining crazyness . lol
There is nothing to stop you using much more than 8 GPUs in afterburner and it will work fine. The limit is on what is switchable from the main interface (limited to 8 ). To adjust the 9th and over GPU, just go into settings and select it there. Also if you synchronise your GPUs it will adjust all, including the 9th etc.