With that size tank, I can't think of any filtration system better suited than a sump.

I've never had a cube shaped tank, but with that capacity, it must be pretty big, so the ability to set up a cross flow with your intake and outlet should still be there for you.

After all, that's one of the greatest advantages of sumps: out from the bottom at one end; back in at the top at another.

The other being that you can use whatever media best suits your water, fish, plants, etc. And, do it with the least costly bulk products.

I also love sumps for their ease of water changes and for a tank that size, being able to run fresh water into the tank via the sump and pre-filtration, makes it a lot less messy.

What kind of FW set-up are you planning? African? Asian? Amazon?