I wonder, though...why didn't you also use Vegas to make the subsequent AC3?
Vegas 8.0 (or at least my copy) doesn't give me control of the AC3 bitrate, the choice of adding Dolby Surround flags to 2.0 mixes, or the ability to author mixes other than 2.0 and 5.1 (like 1.0 for a single channel mono). WAV to AC3 Encoder is much more versatile.