Hi aouimet,
Your fronts are too far apart. On initial setup, I generally advise separation of no more than about half the seating distance or a bit more--try 6 or 7 feet maximum between your front left and right. That way you'll avoid the potential hole-in-the-middle effect that may occur with too much separation. I've never endorsed the equilateral triangle approach--it may work fine in some rooms but certainly not all, and it's better to start with much less separation.
The out-of-phase advice is excellent. That might be the problem, but reduce the separation of your fronts anyway.
Is there any way to try the VP150 below the TV angled upwards? That might help.
If the right front speaker is in a corner, move it away. Corners are almost never good places for any speakers because of the undesirable bass coloration and unwanted reflections.
Be sure you don't use the ONkyo's auto-EQ, which may do nasty things to good, linear loudspeakers like Axioms. You can use the auto-setup until you get an SPL meter and do it manually.
Regards,
