At the end of this article you ask for intelligent playlists that give you (25 most frequently played tracks) minus (10 most frequently played tracks). Well, this can be done rather easily if you set up two auxiliary playlists "MF25" and "MF10" as described and then make a third playlist "MF25-10" with two criteria: "playlist is MF25" and "playlist is not MF10".

However, this is probably still not what you expected: Assuming that you play these songs from "MF25-10" a lot, no new songs will ever enter into "MF25".

I would rather suggest that you
1) define a set of interesting songs, e.g. based on their rating and
2) sort them by least frequently played first.
Thus, you would cover all "interesting" songs and always listen to "new" songs.

If this is still not what you want (never play your favorite songs but always new songs) you might also combine the two approaches:

Let's assume you defined the "LF15" playlist to contain the 25 least frequently played interesting songs. You can then define a "MIX40" playlist as "playlist is MF25-10" or "playlist is LF25".

As you can see, there is almost no end to what you can do by combining auxiliary playlists with rather simple and straightforward logic.

Hope that helps,
Stephan