Install TAudioConverter (is Free Software, GPL2) in wine. This program have the option "Add Folder Tree":
you only need Add the main folder where you have all your collections:
next you chose mp3 in "Presets":
Note: You can chose other parameter you want
Next chose Codec Options
next Start
the place where all files are saved are in HOME in a folder called "TAC":
Working fine in UbuntuStudio, new mp3 are created in this TAC folder keeping folder structure with the options that you put.
(If you wish convert to other format you can)
The wine version is 1.6
CAUTION:
Do not use the option Browse (for the output folders) because not working
From: