Your unit must have more than 32MB of memory for TTS to work correctly. For unit with 32MB (320x240) that TTS will work, it uses old version of NNG.
If a voice file works on a release of NNG product, then it should work on a similar releases (ie: Primo -> Primo, but not Primo -> NextGen) There is no reason to move from Zenec to this release. Zenec can use newer maps just as the map included in this release. Personally I don't really care for NextGen, so I can't help you there. If TTS doesn't work in this release there is problem with the TTS library. Try using the TTS library from Zenec. Which TTS engine are you using? Once TTS is working, then you can worry about TTS Pro.
@oldmatt, he already posted his sys.txt in post #13
To debug/test TTS, I would just put only sound/voice related config in sys.txt
Spoiler: sys
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