Hi Brett
you will definitely need the IR filter to use in conjunction with the RGB filters.
I use an Astronomiks IR filter with mine, you will also need a TF-Adapter which allows you to put the IR filter in the nosepiece. The RGB filter then sit in the slide bar behind it.
You can order the TF-Adaptor from Mogg Adaptors but I would email Steve first to check for availability.
http://moggadapters.com/astro/adapter.asp
Hope this helps.