For my 6X2X2 I use a classic Eheim 2260; it is the largest cannister filter Eheim makes.
Concerning water changes, there are two schools of thought. Mr. Kan of Panda Aquatics actually believes that fewer water changes are better due to the fish coming from slow moving water sources with lots of vegetation and organic matter. This scenario would see strong filtration,however, and certainly no overstocking of the tank with tank mates. Most people seem to prefer a more convntional water change regimen of once or twice weekly, 10-20% each time. I personally follow this second approach.
A good article chronicling one guy's raising of a champion fish is:
I plan to use a Wet/Dry sump for filtration. Likely around 40G's. I've yet to decide on the flow rate as I need to learn more about these amazing fish before I go there. I gotta tell ya....the more I read the more I want one!