Well, on the
Microsoft link for the Runtime, there's two options: x86, which is the 32-bit, and x64, which is 64-bit, so you might want to give it a try by reinstalling both and see if that sorts things out. And apparently they have also have Finnish among the
extra voice languages you can get, which is pretty neat. I kind of wonder how it sounds compared to the Mac version.
That said, going back over the Microsoft Community comments, the issue may lie in the other direction, of needing to have the old SAPI5 installed as well as the newer Runtime 11. If you feel like risking it, Balabolka has a direct download hosted on their own server for the Microsoft Speech API 5.1 installer (apparently removed from Microsoft's own website, as far as I can tell), in the 3rd entry in their FAQ.
ETA: Apparently, SAPI 5.4 is built-in to Windows 7, so that probably isn't the cause.