C# - Select Multiple Items In Listbox From Code?

I have two databound listboxes. The first only shows items that have been assigned to my product. The second listbox shows all available items. What I want to do is select all of the items in listbox 2 that list box one contains.

For example:
ListBox1-
Item 1
Item 3
ListBox2-
Item 1 (Selected)
Item 2
Item 3 (Selected)

Code I have:

List<string> myList = new List<string>();
foreach(ListItem f in ListBoxSourceDetail.Items)
{
myList.Add(f.Value);
}
myList.ForEach(delegate(string n)
{
ListBoxSourceEdit.SelectedValue = n;
});