CORDIC sine calculation can be optimized for generating a slow sinewave by saving state from the
previous lookup.
Alas most audio DACs have high-pass digital filters built in and are hard to drive (48kSPS with 2 24 bit
samples per sampletime).
I don't know of any true audio-quality DDS chips, they are mainly for RF modulation, but I think some
are 14 bit which is pretty good.