Here's what I have on each of my two 325g/1,230l solo Arowana Tanks:
-- 1 X SunSun 704a (no UV). Each canister is level with its tank so not losing much flow from head pressure. They've got one medium course sponge pad and the rest is filled with Ehiem Substrate Pro and OF (Ocean Free) 3DM Tetris media. There's a coarse pre-filter sponge on the intake.
-- 1 X 15-tray (3 levels) Asian-style overhead shower filter. These have medium & fine filter pads plus Substrate Pro, 3DM and also Azoo Active Filter 4 in 1 media.
-- 1 X 36 watt UV sterilizer (which should and eventually will be upgraded to 55 watt units).
-- The OHF and the UV are fed by a 12,000 liter/hr DC pump in the tank, and has a coarse sponge pre-filter on the intake. This pump is dialed down to about 1,800 l/hr for UV and about 2,500 l/hr for the OHF (after taking into account some decent head pressure).
-- 1 X quite big sponge filter + 1 air disc, good back-up in case of power outages.
I also do daily waste siphonings on these bare bottom tanks, so all of my filters stay quite clean -- even after 7 months no servicing of the Sunsun 704's they're really clean (proving canister filters don't have to be so-called nitrate factories).
I'd call the above filtration a bit more than sufficient for Aros' current size, but will likely need to be expanded in the not too distant future. I might try sumps for the first time, as they're certainly best overall, but not sure yet.
For canister recommendations Fluval FX6 seem to be most popular/reliable. Eheim users also love their dependable units. If cost to value ratio is important many are happy with their Sunsun 704's (which I suspect you might already have) and there's also a newer and bigger Sunsun HW-5000 with a claimed 4,600 l/hr and adjustable electronic control (though reviews have been somewhat mixed during 1 yr run production, esp. with regards to the joke 9w UV sterilizer). At any rate the 2 canister filters you have seem enough for a 500 liter tank imo but depends on your bioload.