Yes, you can move the MSI.dat sounds file wherever you want. However, you will need to tell MSI where the new location of the .DAT file is.
To do so, create an alias (OS X) or shortcut (Windows) to the .DAT file and place this alias/shortcut in:
Mac OS X
* startup disk/Library/Application Support/MOTU/MSI
* startup disk:\Program Files\MOTU\MSI
… where startup disk is the name of your system hard drive (usually “Macintosh HD” or “C”).