Warning: Spoiler! (Click to show)
What fascinates me is that the speakers measure ruler flat, it's just the room that's messing everything up!
There's no escaping room treatment, it'd be a waste of good speakers to let them sing like that, hell, that graph makes headphones look flat in comparison.
A 10m x 1.2m roll of 25mm sound absorbing material only runs about USD$130 here, I'd imagine it'd be a fair bit cheaper in your neck of the woods.