ANY way possible to use Membership with an existing Member Plug-in?

Greetings! I am assisting another designer with a site. The client uses a payment gateway that won't work with Membership, so I am forced to work with their current membership plug-in. This amazing POS is called Wishlist. The client would like to set up a different main header navigation for each of their membership levels. While the Membership plug-in does this beautifully, their plug-in has no way to do this at all. I am working with a child of the theme Triden and am having no luck with getting this to work on my own.

I added this to functions: <?php function register_header_menu()
{
register_nav_menu('menu', 'Main Menu');
register_nav_menu('menu-virtual-members', 'Virtual Tribe Members');
register_nav_menu('menu-tribe-members', 'Tribe Members');
register_nav_menu('menu-tribe-leaders', 'Tribe Leaders');
register_nav_menu('menu-90-day-program', '90 Day Program');
}
?>

And added this to the child of the header - to replace the line calling the header function and am getting no joy whatsoever.

<?php global $current_user, $WishListMemberInstance;

$WLMCurrentUserLevels = WLMAPI::GetUserLevels($current_user->ID);

if ( function_exists('has_nav_menu') && (has_nav_menu('menu-tribe-members') || has_nav_menu('menu-virtual-members') || has_nav_menu('menu-tribe-leaders') || has_nav_menu ('menu-90-day-program')) )
{
if ( has_nav_menu('main') )

if ($current_user->ID != 0 && array_key_exists('this LevelNum', $WLMCurrentUserLevels) && has_nav_menu('menu-tribe-members'))
{
wp_nav_menu( array( 'depth' => 5, 'sort_column' => 'menu_order', 'container' => 'ul', 'menu_id' => 'nav', 'menu_class' => 'fr', 'theme_location' => 'menu-tribe-members' ) );
}
elseif ($current_user->ID != 0 && array_key_exists('this LevelNum', $WLMCurrentUserLevels) && has_nav_menu('menu-virtual-members'))
{
wp_nav_menu( array( 'depth' => 5, 'sort_column' => 'menu_order', 'container' => 'ul', 'menu_id' => 'nav', 'menu_class' => 'fr', 'theme_location' => 'menu-virtual-members' ) );
}
elseif ($current_user->ID != 0 && array_key_exists('this LevelNum', $WLMCurrentUserLevels) && has_nav_menu('menu-tribe-leaders'))
{
wp_nav_menu( array( 'depth' => 5, 'sort_column' => 'menu_order', 'container' => 'ul', 'menu_id' => 'nav', 'menu_class' => 'fr', 'theme_location' => 'menu-tribe-leaders' ) );
}
elseif ($current_user->ID != 0 && array_key_exists('this LevelNum', $WLMCurrentUserLevels) && has_nav_menu('menu-90-day-program'))
{
wp_nav_menu( array( 'depth' => 5, 'sort_column' => 'menu_order', 'container' => 'ul', 'menu_id' => 'nav', 'menu_class' => 'fr', 'theme_location' => 'menu-90-day-program' ) );
}
else
{
if (has_nav_menu('menu'))
{
wp_nav_menu( array( 'depth' => 5, 'sort_column' => 'menu_order', 'container' => 'ul', 'menu_id' => 'nav', 'menu_class' => 'fr', 'theme_location' => 'menu' ) );
}
}
}
?>

Not working at all. I do get multiple menu options in the Menu Dashboard, but the menu appears on the screen momentarily while the site is loading and then disappears no matter what membership level I am using. Etch.

OK, for the silly question. Is there any way to use the Membership Plug-in with another Membership Plug-In, so I can use the extremely handy tools for creating a different navigation experience for each user based on their membership level? Wishlist is irritating the heck out of me - and I just want to make it work like your Membership Plug-In.

ANY suggestions would be most welcome!