Any good macro app can do what you want. I use AlomWare Toolbox myself, but I don't have dBpoweramp to test it with. I looked at their website because I was going to try making a macro for you, but I'm not sure which trial version of dBpoweramp to download? Which one is the one you're using?
I use AlomWare Toolbox to close all my windows, using its built-in hotkey of Shift+Ctrl+Alt+Del (but you can change this to anything). Works better than CloseAll because after sending the close signal, any remaining stubborn windows get terminated instead. So you're guaranteed to have all...