Are you referring to the Amber module in Sonar or full version? My experience of piano vst has been a slow learning and expensive one. I own at least 5 different piano vst and make to make the long story short my favourite one is Pianoteq 5 and second is Native Instruments's Alicia Keys.
The amber module that come with sonar is definitely the best piano included in sonar. I have not try the SCDSF steinway. However I have heard a demo of DSF's HD yamaha and steinway and felt that they are not realistic enough dynamically.
I got my Native Instruments's Alicia Keys for only 50 bucks during their nov or dec sale. It's coming soon after thanksgiving so watch out.
https://soundcloud.com/musichoo/remembering-youThis is performed with Native Instruments's Alicia Keys.
https://www.youtube.com/watch?v=1GywenwtI6g&list=UULr5jMKP7D9ky8ehrHF2BGAThis is performed with Pianoteq 5.
Cheers