How can I filter the Directory listings page results by taxonomy?

I need to let users be able to filter out the results in the listings page by selecting taxonomies. I tried using the Query Multiple Taxonomies plugin to do this, but it doesn't work very well with Directory. It 404's when I choose a listing_category. (You can see it here http://growdevelopment.co.nz/tonga/listings/) Is there a way I can make this plugin work with Directory, or is there a preferable method of filtering Directory listing results that I should be using instead?