Just out of curiosity, have you tried to toe them in a bit and create a little more air in the back on one side of the speaker?

One more thing. If you do have to go with an EQ, try and find a Yamaha. You will be happier with it then the one you are looking at. I still think if you tweak the placement, you can fix it without the EQ but who knows for sure. I'm also assuming that you don't have a loudness button on by chance do you? Are you running everything flat? ie no treble, no bass?