There is any way to get my foobar library grouped alphabetically like in the picture? At the moment I can sort by artis=>album and I would like to do it by letter=>artist=>album

I use Library Filter, which comes with PanelsUI(can be used with CUI).

Can look like this.

Letter
$if(%artist%,$left(%artist%,1), -= UNKNOWN =-)
%artist%
%album%

First row is the caption, the second is the first filter and so on.
It may work with other panels too, the filtering code.

In preference > Media library > Album list

Add a new column using this code

$caps($left(%artist%,1))|%artist%|%album%

Should do exactly like in the pic.

Wow!!!! Thanks a lot buktore!!!