I just went to Theo's site and checked the QHY9 page and noticed that 2" LRGB are no longer listed as part of the package. You may want to buzz him and ask if the LRGB filters are still available separately? Also check the QHY forums for filter brands and info.
Either way you don't need to worry about filters having issues with QHY FW or QHY9M. All 2" filters should fit so buy whatever brand you want down the track and go crazy!
TC