I assume that festival falls into the "too large " category, or possibly the too much CPU time required?

Ohhhhhhhhhhh yeah. I took a stab at Festival but it doesn't even come CLOSE to running in the Empeg's memory footprint. So CPU isn't even an issue.

Festival is the Emacs of TTS systems. It uses a bunch of LISP files to define its various diphone and speech engines... It's amazingly configurable and tweakable, but massive and bulky. The author saw this as an opportunity to make the same kind of thing work on smaller platforms, and that's Flite. LISP is replaced by tight C code. I think it's a great effort.