Hydor Flo device in place of the stock water nozzle. Not extra flow, but it redirects water in a wavelike fashion. I've also heard Rio pumps are failure prone, you might look into getting a maxi-jet 900 or perhaps a 1200. I run a 900 in my NC12DX, its rated for a bit more than 200gph.
Go with it if you've had good luck, I'm just passing along what I have heard, I've never used them personally. The Hydor Flo I DO have though, and I really like it. And the stock pump in a Nanocube 12 is 106 gph, not 84. IS yours a 12?