same company selling it on trademe are selling it on sella for $100 less. good practice to source something on trademe, then check sella. a lot of the time the same company has listings on sella for cheaper because they dont have to pay fees.
im also in the market for subs, just bought a wharfedale POWERCUBE 10 off trademe second hand for $250, really good condition. need one more for the bedroom was looking at that onkyo skw-770 off sella :) (no rush to buy, dont need it for a couple months, so ill wait for another bargin).
sadly, i know absolutely nothing about subs though. the wharfedale one is the same one as my parents, so I know its good IMO, and on jbhifi they cost $400 (probably could get slightly cheaper, but pricespy they've never been on special). and since i need two, dont want to spend a lot of them.