Game Extractor will dump the dyn files.
It will not repack them.
Might be able to figure out how to repack by studying the format as the .dyn is not compressed.
http://www.watto.org/game_extractor.html
Here's the file format specs for the .dyn files
20 - Header (Dynamix Volume File) + null
2 - Unknown
4 - Unknown
2 - Unknown
2 - Unknown
2 - Unknown
4 - numFiles
// for each file
4 - Unknown
// for each file
13 - Filename (null)
4 - File Size
X - File Data
0-3 - null padding (to a multiple of 4 bytes)