You also inquired as to my thoughts on Darth Maul's "At last we will reveal ourselves to the Jedi, at last we will have revenge." This is one of the coolest lines in the PT, and ties into the titles of Episode III. Of course when you look at just the movies, it is never explained what they want revenge on the Jedi for, other than the fact that they're evil, and I think this is what you're getting at. I suppose I could argue it adds mystery to their motivations, a good thing, but like Syfo-Dias, this "mystery" is never answered on film. Maybe there is a way an explanation of the Jedi/Sith background can be incorporated into Episode I, but I haven't a clue how to do it. My best suggestion is to have Anakin ask Qui-Gon what a Sith is and he explain it to the boy, on the landing platform in place of the midichlorine discussion. The logistics of this are beyond me at this point, barring traveling back in time to the production of TPM and filiming the scene with Jake and Liam. There's only so far dialogue from other sources can take you, but perhaps we can cobble something together.
As for Darth Maul/Grievous himself, I'd want to use as much dialogue of his as possible. Whoever it was the dubbed his voice was awesome, and it sure would be great to get him to dub Grievous for us in Episode III.
The tone poem is excellent, but where can you put it? The first place that springs to mind is his arrival on Tatooine, but would a Sith talk/think to himself like that? And hearing a characters inner monologue isn't a Star Wars technique, so I don't know how to approach this exactly.