Thought I'd give that program a try. FYI, it does install the voice as a SAPI5 voice compatible with plenty of other programs (including EDDI).
To use the voices more broadly, the following may also be helpful:
The Ivona voices are 32 bit voices so if you're using 64 bit windows like I am, the default system dialog doesn't show them... they have to be selected by opening a 32 bit Windows configuration dialog here: %windir%\syswow64\speech\speechux\sapi.cpl
That's the same window I get when I click on Speech Recognition in Control Panel and then Text to Speech. I have British Amy selected as my default speech voice but there are also Zira And David (the voices that ship with Windows 10).