I own the 5.3s and am seriously considering trying the Sonatinas. I've heard them at shows and my impression is that they may be better balanced overall and easier to place in a room(5.3s can be bass heavy in certain rooms and/or with less than optimal setup--they need lots of room to really open up). I think the Sonatinas have a more "neutral" sounding midrange, as opposed to the 5.3s that have a more rich and full sounding midrange. They both are exceptional at pulling off the disappearing act.
Silverline does make a center channel, but I don't think it's perfectly matched to the Sonatinas(doesn't have the dome mid) but I haven't heard it and it's probably at least very good. The Soliloquy center uses the same drivers as the 5.3.
All that said, at the same price point I think I would choose the Sonantinas, but I have not heard them side by side with the 5.3s so this is really just an educated guess, for what it's worth. Best of luck.
Tim
Silverline does make a center channel, but I don't think it's perfectly matched to the Sonatinas(doesn't have the dome mid) but I haven't heard it and it's probably at least very good. The Soliloquy center uses the same drivers as the 5.3.
All that said, at the same price point I think I would choose the Sonantinas, but I have not heard them side by side with the 5.3s so this is really just an educated guess, for what it's worth. Best of luck.
Tim