Multibinding Multiselection ListView

Question

OK I have a weird one here. What I am trying to figure out is how to have one listview, populated by an ObservableCollection, update another ListView, populated by another ObservableCollection, based on the first listview's selection and then use a valueconverter to check or uncheck a checkbox based on the selection combined with the current item in the second listview. This part I somewhat have working by using multibinding, but the part that has me stumped is when I check or uncheck an item in the second listview I need to be able to grab that event and all the currently checked items in that listview an update a database field based on that.

I know this may not make a lot of sense and I'm struggling on how to make it clearer, but below is the xaml for the two listviews and the code for the converter. I can see that when I check or uncheck a box in the secodn listview that the converter tries to do the ConvertBack method which blows up, but if I set it to just return null then the code no longer blows up, but the checkbox is highlighted in red like a validation error has occured.

I am not even sure that multibinding is the way to go here and I have looked at Josh Smith's multiselection listview stuff, but with the conversion needed I can not see how to implement that successfully either.

If anyone has any ideas I would greatly appreciate it. Also my apologies if I didn't explain my need very clearly, but I am hoping with the chaotic description and the code you can kind of see where I am going with it.

Thanks in advance!

First ListView that feeds the second one

<Grid>
                <ListView x:Name="listRule" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" Margin="3,3,3,3" ItemsSource="{Binding RuleListing}" exts:Selected.Command="{Binding RuleSelectedCommand}" SelectedIndex="0">
                    <ListView.ItemTemplate>
                        <DataTemplate>
                            <StackPanel Orientation="Horizontal">
                                <TextBlock Text="{Binding Path=DisplayName}" ToolTip="{Binding Path=Expression}" FontWeight="Bold"/>
                                <TextBlock Text=" ( "/>
                                <TextBlock Text="{Binding Description}" FontStyle="Italic" />
                                <TextBlock Text=" )"/>
                            </StackPanel>
                        </DataTemplate>
                    </ListView.ItemTemplate>
                </ListView>
            </Grid>

Second ListView with converter and multibinding

<Grid HorizontalAlignment="Stretch">
                <Grid.Resources>
                    <converters:RuleToRoleBooleanConverter x:Key='RuleRoleConverter' />                        
                    <DataTemplate x:Key="RoleTemplate">
                        <Grid HorizontalAlignment="Stretch">
                            <Grid.ColumnDefinitions>
                                <ColumnDefinition Width="1*" MinWidth="200"/>
                                <ColumnDefinition Width="20"/>
                            </Grid.ColumnDefinitions>
                            <TextBlock Text="{Binding RoleName}" HorizontalAlignment="Left" Margin="3,0,0,0" Grid.Column="0" />
                            <CheckBox HorizontalAlignment="Right" Margin="0,0,3,0" Grid.Column="1">
                                <CheckBox.IsChecked>
                                    <MultiBinding Converter="{StaticResource RuleRoleConverter}">
                                        <Binding ElementName="listRule" Path="SelectedItem" />
                                        <Binding Path="RoleName"/>
                                    </MultiBinding>
                                </CheckBox.IsChecked>
                            </CheckBox>
                        </Grid>
                    </DataTemplate>
                </Grid.Resources>
                <ListView Name="listRoles" ItemsSource="{Binding RoleListing}" HorizontalAlignment="Stretch" VerticalAlignment="Stretch" 
                          SelectionMode="Multiple" ItemTemplate="{StaticResource ResourceKey=RoleTemplate}">
                    <ListView.ItemContainerStyle>
                        <Style TargetType="{x:Type ListBoxItem}">
                            <Setter Property="IsSelected" Value="{Binding Mode=TwoWay, Path=IsRoleSelected}"/>
                        </Style>
                    </ListView.ItemContainerStyle>
                </ListView>
            </Grid>

Value Converter

public class RuleToRoleBooleanConverter : IMultiValueConverter
{
    public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (values[0] != null && values[1] != null)
        {
            string expression = ((EliteExtenderRule)values[0]).Expression;
            string role = values[1].ToString();

            if (expression.Contains("R:*") || expression.Contains("R:" + role))
            {
                return true;
            }
        }
        return false;
    }

    public object[] ConvertBack(object value, Type[] targetTypes, object parameter, System.Globalization.CultureInfo culture)
    {
        return null;// new object[] { (bool)value, null };
    }}