yes, you could certainly use a DAC. The ideas that people are putting forth are about using one or 2 pins. A parallel DAC will take 8-10-12 pins while a serial DAC will take fewer pin but is a bit more complex to use. I would not use parallel with a uC but rather a serial one. However, I didn;'t get the sense you needed all that great quality.
Look at the Roman Black page - his algorithm actually produces fairly good sound quality with 2 output pins.
By the way, a DAC doesn't step the voltage up or down but rather you tell it what voltage level to output, thus tracking the waveform you are trying to reproduce.