Sorry you are having difficulties.
Here is exactly what I did…
In the tagline, I entered the following:
Text Line 1<br />Text Line 2
I modified parts/class-header-menu.php as follows:
On line 82, I changed the following so the tag line html characters get translated correctly in a desktop browser.
<h2 class="span7 inside site-description"><?php bloginfo( 'description' ); ?></h2>
to
<h2 class="span7 inside site-description"><?php echo wp_specialchars_decode(esc_attr(get_bloginfo( 'description' ))); ?></h2>
I also modified parts/class-main-header.php.
I changed line 181 so the tagline with html characters gets displayed properly when viewing the site on a mobile browser.
<h2 class="site-description"><?php bloginfo( 'description' ); ?></h2>
to
<h2 class="site-description"><?php echo wp_specialchars_decode(esc_attr(get_bloginfo( 'description' ))); ?></h2>
Hope that helps.
Mike