how to reinstall instrument files (.cst) after a backup?

I've had to do this four or five times now. I just spent two hours trying to search this on the forum and came up empty. It would be nice if someone could publish the definitive guide to this problem and make it easy to find, because it happens consistently every time:

Every time my hard drive crashes, Garageband will not show my saved instrument files -- mean the ones that show up in Garageband under the path: Track>Show Track Info> Software Instrument tab. The old hard drive was fully recovered, so I know they have to be there somewhere. I've searched these paths:

Users/Me/Library/Application Support/Garageband/Instrument Library

Users/Me/Library/Audio/Sounds/Banks

HD/Library/Audio/Sounds/Banks (this is empty)

I've downloaded my old banks off my backup hard drives.

All I seem to come up with are .sf2 files, which are instruments, yes, but not the ones that you create yourself and save in the Garageband path above when you hit the "save Instrument" button at the bottom right..

So the simple question is: when garageband opens your newly saved instruments, where does it find them? And in what file format are they? And how do I recover the old ones? Thanks