Does the middle name represent a tag that isn't filled yet?
In that case I suggest that you first fill the tag with an action "Guess Value" und later create the directory and move the files with another action.
It would MUCH easier if you could fill at least one field with the data you want to use for the filename conversion. Because otherwise you have to fiddle about with $strstr() and $mid() and stuff.
So:
Use convert>Filename-Tag
with the mask:
%dummy%-%artist%-%dummy%
This puts the middle part into ARTIST - but you can delete that safely afterwards.
Then use Convert>Tag-Filename
with the mask:
%artist%\%_filename%
This should move files to the new folders.
Then select all files, go to the tag-panel and select in the field ARTIST from the dropdown list and press Ctrl-S to save the modification which is the deletion of the data in the field ARTIST.