The easiest way to achieve this is to create aliases for the drive's or folders that hold your sounds. You can then place the alias into the Mach 5 Sounds folder. To do this:

First locate the folder or hard-drive's icon that you want to make the alias of.
Hold [control] while clicking on the icon, you will get a dropdown menu in which "Make Alias" will be one of the options, choose this.
You will then see the alias for folder or drive.

Simply place this alias inside to the folder you have designated as your Mach 5 Sounds folder and repeat the process for other drives or folders.