Well, absent any replies I dug further into this and thought I'd share what I found, if only to save someone else the bother later on.
1. EDDI apparently has its own speech engine; this explains why they can do the reverb-style voice processing internally.
2. Yes, you can pass commands thru EDDI to get the voice processing effect. Pfeil has some past replies on the subject on this forum. But if you are not using EDDI to play elite dangerous, those steps seems a bit cumbersome. Also, it seemed to me that the responsiveness slowed down a fair bit for me; your mileage may vary.
Bottom line: if you absolutely had to have that voice processing, EDDI can give it to you, but at a cost in response time and in re-coding your commands to run thru an External Plugin.
The other angle I examined was seeing if Morph Vox Pro could ingest the voice audio from the Microsoft TTS engine and apply a real-time distortion just as it would if you were speaking into a microphone. MFR Screaming Bee told me there was no way for their software to capture the TTS audio. Oh-for-two on trying to overlay a very soft bit of reverb on the Ivona voice (which to my ear just smoothed it all out and actually sounded more human).