@Muskillogemi,
I raised your TTS problem with Kovid
in the calibre development form. There's no magic solution, I'm afraid, but there are a couple of suggestions from @rantanplan you could try.
Unless you know different, I can't help thinking that the installation of the Cereproc Voices may have made a permanent change to your Windows which is not compatible with the older Ivona Voices on a 64bit PC.
I think you said that the Ivona/Cereproc Voices are co-existing quite happily in 32bit TextAloud. So something else you could try is to install an additional copy of calibre Portable, which you can find on the standard calibre Download page.
You can install it on a pen drive or just somewhere convenient on any connected hard disk. Keep it away from your main calibre installation. All books/settings for the Portable version are independent from those for your main calibre books/settings. Calibre Portable always runs as 32bit, even on a 64bit PC so Voices should be accessed from the same part of the Windows registry as TextAloud is using.