Herbie,
I own a music store in Los Angeles and I sell both the Yamaha andthe Ketron products. From my customers experience, the Ketron SD1 has been used more in clubs around my area for it's great sounds and exciting styles. One of it's big strengths is in the Europeans sound and style catagory. The Schlager style is in the catagory called Party in the SD1 and there are 3 intros and ending and 4 variations. There is no style in the 9000pro called Schlager although I'm sure one could be made or converted. Because Ketron is a European made product (Italy) and Yamaha is a Asian made product (Japan) I think the strong European influence can be found in the Ketron products. One of the big differences is in the Accordian catagory There are 18 different accordians in the SD1 and only 8 in the Yamaha. I also think the style tracks in the SD1 are much more exciting for an audience to listen to when it comes to contemporary styles such as funk, rock, hip hop, etc. Both keyboards are similarly priced. I sell both of these and would be happy to answer any questions you might have besides what you have already asked.
George Kaye
Kaye's Music Scene
Reseda, California
818-881-5566