Header Create Sub-section with different layout.

I am building out a new site for a client and right now, it has the sort-of ‘standard’ layout of (1) site logo far left, (2) name of the company and (3) main nav menu spread across the width of the header container. However, they now want to add a couple of top-line menu items which is really causing the nav menu to compete for space.

My goal was to create a “sub-section” beneath the top line header, remove the main nav menu from it and add it to the second row and center it on the screen. I DO see that I can add a second row to the header which is nice, but the problem is that it inherits the column structure of the first header row (so, three columns at first, and if successful, it could become two columns. Is there any way to make it such that the two rows of the header could contain differing numbers of columns?

Thank you for any suggestions that you could offer. Cheers!