Another thought would be to go to Home Depot or Lowes or Ace Hardware and get a clear acrylic magnetic vent deflector. It sticks to the vent cover with the magnets and deflects the flow of air. Originally made for under dressers and curtains, it should alter the flow of air enough to give you some more calm areas.
Here's what I'm talking about
Deflect-OŽ Unbreakable Air Deflector (50) - Air Deflectors - Ace Hardware