Regarding PRELUDE and INTRO tunes...
There are two games: One Must Fall, and One Must Fall 2097. Prelude and Intro belong to the first. There are only 7 songs in OMF2097 which are the S3M format ones in this archive.
Rated 10 because of the amazing quality for the small size.
I'd also like to add that the original format is MTM and has been included in AMP:
The songs of the original format sound way better. The ones in the Mirsoft archive suffer slightly from inaccuracies of the conversion process. Thank you C.C.Catch!