That's not true imo, 2 FX6 and even 1 HOB would easily filter a 180, unless perhaps if it was very heavily stocked.And they said that 2 FX6's and HOB wouldn't be enough. Is this not true?
And no, your tank doesn't absolutely need air stones but personally I never run tanks without them and at least 1 sponge filter, esp. as I live in a hot place. I hook them up to ac/dc air pumps so that if the power ever goes out (whether I'm home or away) they turn on automatically. Air stones are also good for drawing current up from the bottom of the tank to the top, which canisters and HOB don't really do so much.
Some don't like the look of them but pound for pound nothing really oxygenates a tank better than a simple and cheap air stone. I also like to have a sponge filter -- if the power went out for a longer time and all/most of the beneficial bacteria in your canister or HOB died off, a sponge filter can help to save your fish.