It looks like those place the speakers into the fresh air vents which of course blocks the vent. If you wanted to keep your fresh air vent down there, you can put speakers into your stock kick panels with some careful locating(using cardboard stencils), although they can't be too big. I think mine were 4.5". There are some 'Kick Panel Restore' photos of how I modified mine to fit speakers at the link below. Photo 'Interior Completed 11' shows the final product.
http://www.69camaroproject.com/gallery-interior.htm
Just an alternative to possibly save you some cash and keep your air vent.