The efficiency of K-1 is irrelevant. You won't have 10 times more fish in your 120 than anybody else has in theirs, will you? You gonna put stingrays in your 120? You can support the bio-load of a 120 gallon tank with a handful of pumice stone in a small canister filter. With a few pot scrubbies. It is very possible you can have a healthy tank with no bio-media at all.
You're making this way harder than it needs to be. If you like building exotic filtration systems in sumps, then go with K-1 and let us know what tricks you came up with to get it quiet. K1 is cool.
But, if you want a low-maintenance reliable filtration system that keeps fish healthy in your tank, K1 is unnecessary. Drop a bag of pumice stone, seachem matrix, pond matrix, or some lava racks in the bottom of the sump and enjoy your fish.