I am adding an external mp3 as a narration for each screen of a presentation.

There is an obvious delay as a screen is revealed as the external mp3 starts
to stream.

Is there a way to simultaneously begin loading each of the mp3 once the
presentation begins with the goal being no delays with the narration.

For example,

Slide 1 is revealed - narration for slide 1 begins (Concurrently, narration
for slide 2, slide 3, etc downloads so that there will be no apparent delay
when slide 2 is revealed (slide 2 narration begins immediately).

I would suggest using the mediaDisplay component with a single MP3 file.
Assign cuepoints indicating when to jump to the next screen. There will be a
single delay in the audio for the MP3 to begin playing. Screen changes do not
interrupt or delay the flow of the audio. Timing is reliable. If your screens
contain large bitmaps, the initial delay can get long.

I'm using MX 2004 and jumped to that from Flash 5, so I don't know when this
capability was in the original Flash MX.