After a long time I found some time and reworked all scripts. Now you have the option to use each module independently or together, whichever you prefer. The files are here:
amazon.ifs: Amazon plugin
cddb.ifs: CDDB plugin
freedb.ifs: FreeDB plugin
cddb_freedb.ifs: CDDB & FreeDB plugin together
UAmazon.pas: Amazon core module
UCDDB.pas: CDDB core module
UFreeDB.pas: FreeDB core module
UMusicCommon.pas: Common module
You also need StringUtils1.pas, which is part of the AMC install, I think.
EDIT: Or you can just download
this zip file which includes all previous files.
All .pas files are mandatory, .ifs files are plugins and you can install all of them or just one, as you like.
Please note that these scripts aren't thoroughly tested and there may (and probably are) still be bugs, so please inform me if you find one.
If you will use combined CDDB and FreeDB script then results from each will be displayed in one pick tree, each under different root. I don't think there is a way to collapse the pick tree, so you must collapse it yourself or scroll all the way down to see results from FreeDB.
Regards