Ok.
banners=bad when trying to "sqeeze" 800 width unless you move them to the TOP of the page by themselves.

So far with the total width of your logo and banner image is
932px
You can find this out by right clicking each of those images in your header and checks it's "properties".

Unlesss you lose or move the banners or make your logo image a lot smaller, 800x600 theme size is not in your future.

mikem