The 661 gives a fair anoint of isolation, it fits tight... may even work to record live with, much better bass.. then it's look alike 7506.. the sound is more produced, i would not mix with this can ... it makes a bad mix sound like a freaking hit... it is ear candy to the max... i thought the 7506 fit that bill... Anywho very enjoyable listening headphone.

The 668B is smooth, has a more raw sound... but semi open .... any of the 662 series give good isolation, and true to life sound... but vast EQ difference in the 3 the 662 is like deep lows to hell and a smooth wide midrange sea, ( kinda nice pleasant actually ) and then highs that send you to the moon... i better talk about the other 2 L8R ... actually just wanted to see if i could post something... like the series.. great studio cans. Doyen