rmteo,
You are correct an spi dac is not suited for generating sine waves. My goal was to
learn how to use this dac, which I did. I have used the AD9835 and AD9850 which are lower
resolution versions of the AD9837, which you mentioned. The 28 bits of resolution is fantastic and
I may request a sample since Digikey and Mouser don't stock the AD9837 yet.

Regards