If you liked your AL-III's you will also like Magnepans. I have not heard 1.7's, but my MG-IIB's were really nice sounding. They didn't have the ribbon tweeters like the IIIA so the highs were slightly dull. The newer 1.7's should be better in that dept. What I really liked about them was the pinpoint location image they generated. I heard a similar sound with Charlie's self-built ESL's at Carverfest last year, in fact his were a bit better than I recall the Magnepans being.
Having said all of that I absolutely love my Carver ALS w/60" ribbons. They get the bass note that's lacking in the Magnepans. Magnepans have a very fast/realistic mid-bass note but don't carry it deep enough. Sunfire TSW should fix that.