you could always go for something like 3x ac110 HOB filters, and that should do it too.
WTF!
So, you go from a 80 gallon sump which can hold 110-240 liters of media, to two Fx5 which will hold 10 liters of media @ 1200 GPH, to 3 AC110s which in total will hold 3 liters of media @ 1350 GPH. I am not saying they won't work, but you tried telling the guy that 80 gallon sump is the way to go and he should actually go bigger and then you tell him to get 3 Ac110s that hold 3 liters of media altogether....
To the OP. DO NOT LISTEN TO THIS GUY!! He has no idea what he is talking about!!