Matthew's Mixes Episode 2 is a collection of music compiled specifically for the original Doom. The music replaced all music on Episode 2: The Shores of Hell. Also, three replacements for the title, intermission, and victory screens. The zMatthewMixesEp2.pk3 was compiled to be used with the Doomsday Engine port. However, it can be played under the Zandronum port as well. All music present in this .pk3 was composed and performed by Guy Matthew Babin, except Movement 5 which was performed by the computer. The music has a soundtrack feel for it. They were carefully selected for Doom playing. If you want to know about the composer, you can view his webpage at www.babins.org/Guy/.
A WAD version can be downloaded here: Doomworld.com
Whats the difference about files delivered in a pk3 instead in a WAD file?
I know the PK3 file system from Jedi Knight 2 (Quake III Engine).
I believe Doomworld site only accepts WAD version for the upload. There is no difference in the music selections. They are both the same.