Mark,
I am not familiar with Kurzweil equipment, however I have owned a great deal of Yamaha equipment and currently own a Yamaha EX5. I cannot help you out on the comparison of Yamaha vs. Kurzwiel, however, I think for a minimal amount of money, you get quite a bit more in the EX5 rather that the EX7. So, if you decide to purchase Yamaha, you may want to consider the EX5 - last I checked the difference in price was less than $300.
Good luck and let me know what you decide.
Mike