Grounding DAC chip tweak

What are you trying to achieve? Grounding of a DAC chip, as with any other active IC on a PCBA, isn't a tweak; it's done by the engineer(s) who designed the product.

After upgrading the ground wiring on my dac that feeds the board and IEC, I was able to lower noise floor and remove grunge from the signal. In reading another thread, further improvements can be obtained by adding a copper double sided board on top of the dac chip with a wire attached and taking it to ground. This seems to lower noise even more according to the individuals who tried it. Has anybody
tried this?

It is not so much grounding the DAC chip as shielding it. Just get some copper shielding and fit it over the entire DAC board and all its chips. Run a wire from that shield to a ground plane and you've got it covered.

In effect you are creating a partial Faraday cage. If you bend the edges of the foil downward you can shield even more.

Enjoy,
Bob