The usual endless upgrade spiral. First I got my Mirage 350s and loved them. Then I upgraded my electronics to Cambridge Audio Azur, and heard a very definite improvement in SQ. Finally, I read that Cambridge recommends the S30s for use with the Azur electronics, and new I had to try them.
I frankly doubt that they can end up replacing the Mirages (which sound fabulous), but I won't know that until I have heard them. It never hurts to have an extra pair of nice minimonitors, in any event.