Steel- I haven't had a chance to hear the SongBird, but I've got to think the TL design would offer an excellent sound.
I do have SongSurround I's that I am using with my SS8's. Jim had suggested I would be very satisfied with these, and I am. When I read your question, I decided to hook up the SongSurrounds as my mains and see how they sounded. Frankly, they were excellent by themselves. With the Rythmik sub, even better. For me, I could be very satisfied using them on their own long term.
I would say that if you would like a floor standing speaker, the SongBird would be a great choice. If you are looking for something smaller, or for bracket mounting the SS1 is a deal.
I'm sure some of the regulars who have heard both will have some good insight, as would Jim once he is back from AXPONA.
-Ben