I don't think that the OP asked for that, and I certainly didn't have that in mind. I was hoping to calculate the no-filtering THD, which seems a lot easier to calculate. I can always do a SPICE simutation to figure it out for a particular DAC and filter, but having a formula and figuring out the reasons why the formula works is always a big help in getting a deeper understanding of a circuit. And it's an interesting puzzle.
Leaving off the filter, how did you calculate the 0.02% and 3% THD figures? Did you use the "multiply bits by magic number X" method posted elsewhere?