I have a 265G and am Very Very over stocked with 9 Oscars, a Rhino Pleco, a Sailfin Pleco, a Featherfin Catfish, 2 Pangasius Catfish, 2 Bushynose Pleco, 2 Electric Blue Acara, 1 Electric Blue Jack Dempsey, and a Mated pair of Convicts with Fry as we speak.
I'm filtering with 3 Fluval FX5s, 1 Eheim Classic 600, and a Turbotwist 36W UV Sterilizer... And gravel vac and swap 50% water weekly.
Oscars are by far my favorite fish to keep and what your hearing here is 100% correct they are the messiest fish ever.
Always over filter. If you want to get rid of the Hob I would suggest you scour craigslist for a Fluval FX5 or an Eheim Pro III. Once the second canister is established reconfigure your 406 to a mechanical/ polishing canister. Stay on top of your water changes and honestly a strategically placed Sponge filter and Powerhead wouldn't hurt...