The Tidal speakers do have an amazing finish, and I'm sure from what I have read that they sound very good too, but I haven't heard them, The SCM 150 I have heard, and for a good long audition at a dealer in Connecticut. I think that they are two different animals, from what I have read about the Tidals. They are both supposed to be accurate and transparent, but I don't think that the Tidals will be able to match the dynamics of the ATCs.
This past summer, I went to the Scottsdale Speakerfest with a friend, and we both agreed that a smaller ATC floorstander was the star of the show. I can't recall the model number, but I think that it was around 7k.