Centralize and avoiding resize this huge header image on Twenty Eleven

I’ve got an awesome header idea, but I can’t get it done. My WordPress is running locally, so I can’t show you what’s my exactly problem. I’m already using a Child Theme of Twenty Eleven, and I would say my CSS knowledge is “intermediate”. Here’s the problem:

I wanted a full width header, both for the menu bar and for the image. Something like this: http://capinaremos.com/. On this specific site, he used a 2000px image as a header, but it’s centralized so you can see it if you got a smaller resolution, say 1024px wide. Here’s the header that image that he used: http://capinaremos.com/wp-content/themes/booger/styles/capinaremos/bg-overlay.png. So, I created a 2800x130px image to use as header image, but I couldn’t centralize it. Some things I did and its respective results:

A) I changed the header image size to 2800×130 on functions.php, and since both header image and the menu bar are originally aligned to left, so I just added this on style.css:

#branding, access {
	margin: 0 -900px;
	min-width: 1000px;
}

Which centralized the image, but I couldn’t see the search box (default Twenty Eleven’s serch box, which should go on the header image) and the menu links anymore.

B) If I set the min-width to 100% and max-width to 2800px, the image resizes itself to the default 1000px wide, which reduces the height to something like 40px, and it isn’t what I want.

And in both ways, I got this huge 2800px image, that I can scroll sideways to the rest of it. I want to centralize it and limit in some way (min-width: 1000px) so people with low and high resolutions can see it without any kind of resizing. Someone got some ideas on how to solve this? I would appreciate that.

Thanks in advance.