Yeah, i know. But what do i have to enter there to group compilations correctly? I have no clue.
You can enter in any code you want to take advantage of the metadata you want to use. For example, I have mine really simple such that when an album is not VA it will display
Artist - Album (Date)
and when it's VA it will just display the 'Album (Date)' part, and then in the track column (I don't keep an artist column) it will give the specific artist of each individual song after the title. I do this with
$rgb(61,129,193)$if($strcmp(%album artist%,VA),%album%[ '('%date%')'],$if2(%artist%,<no artist>)[ | %album%][ '('%date%')'])
in the NG Grouping part, and for my track column I use
$if(%isplaying%,$rgb(61,129,193,61,129,193)
$if($strcmp(%album artist%,VA),%title%$rgb(128,128,128) / %artist%,%title%),
$if($strcmp(%album artist%,VA),%title%$rgb(128,128,128) / %artist%,%title%))
From there just make sure that your songs have similar metadata. For example, if you have a VA album and some of the songs have %date% (and you display %date% in your grouping) information and others don't, or different values, NGPL will split them into multiple groups.
The $rgb() values in my code are specific to my config' obviously, but I hope that gave you some ideas or something you could work with at least. If you want some further ideas visit this page to see what other little things you can do.