Commercially available pHAT DAC costs about $12 and adds just a headphone jack to your Pi Zero. On the other hand, the $14 Adafruit Speaker bonnet provides, two 3W audio channels for the loss of the headphone jack. The DIY HAT shown below strikes a balance between both the commercial HATS, by providing both the headphone output, as well as speaker outputs. Whats more interesting is the cost of implementation of the DAC, which is about $6 or $7.
So, at quarter of the cost of two DAC's you are getting the functionality of both.
Connect the Left, Ground and Right pin from I2S DAC to Left, Ground and Right pin of the PAM8403 amplifier. Also connect the 5V and Ground pins from Pi to the PAM amplifier's supply terminals.
For installation of the homemade DAC on a Raspbian, you can use the pHAT DAC's one line installer command:
curl -sS https://get.pimoroni.com/phatdac | bash