If your water is clear and your fish (and you) are happy (and water conditions are appropriate) I wouldnt change a thing, but to answer your question...
I would not run 6 canisters on any household tank. The trick is to create lots of filtration without creating too much current. You do this by using different filtration methods, not by using 6 of the same filters.
I did it by using power heads and sponge filters to power my usj (600gph) as well as a spray bar returning filtered water above the tank (145gph). My Magnum (350gph) is the only filter on my tank that creates much current.
600gph + 350gph + 145gph = 1095gph / 75 gallons = tank volume X 14.6. Now we could do some more math and see that with rock and substrate in my tank im not actually holding 75 gallons so i am actually a little higher than tank volume x 15, with enough current to keep my fish healthy but not so much to stress them.
Tank volume x 15 is not difficult to achieve with a little creativity.