I know I once found an ac3-track of the 1991 mix which contains the surviving narration by Deems Taylor. If I'm not mistaken, there was another Fantasia-project like yours here on the boards, and the link could be found in that thread.
Apart from that, I'm not really into the technical stuff of ripping and muxing. But I do wish you good luck on this project - the result should definitely be worthwhile!