That would be up to the maker of your model card as to what it supports. You gave no information on your maker or model. While AMD has reference specs that doesn't mean makers follow them. In fact most cards are not reference models. You should be able to get this information from your card makers website or their support department. If you want one of us to help please reply back with the model and maker.
I can tell you that I googled this and tons of people are complaining that 2 monitors work but not 3. That doesn't mean it can't work as I don't know what your specs are but going to 3 may require a very specific setup and possibly certain adapters to do it.