Lets not steer this topic into something about the pros and cons of Delta Sigma DAC,s oversampling etc.. We live in a wonderful time where we can buy DAC chips that have very high dynamic range, with high SNR and very low distortion for <$2.
To the OP. I understand wanting to get things "right" before committing to a PCB design - no-one likes having to add extras on - so it is product to add foot prints for output filters, specifically opamp output filters. You could always just not populate these if you add a foot print for a jumper - maybe a 0805 0-ohm resistor - to bypass it straight to the output.
Puting RC filters in series - using two caps and two resistors can indeed produce a two-pole filter with a steeper cut-off, but because they are not buffered, their gain is reduced because the second RC filter isn't driven by a zero-impedance output, its the output from another RC filter which generally has a high impedance. A 2nd order filter using an opamp is generally more accurate, and you can easily make this a 3rd order filter with a simple RC on the output (which is driven by the opamp = low impedance output).
As with all things audio, one can get carried away trying to get things perfect, but then you'll never get a PCB made. I'd say, find a similar design on TI's website, copy it for your board, with the facility to bypass this.