Just an update with my own experiences switching to DX9 instead of DX11. I did that yesterday. I came in game and first wandered around Firmament where the SE from all the crafters usually stuttered, and heard no stuttering. Then I spent a long time running Trusts with no audio problems. Then I started doing daily Roulettes. When I got to the Alliance roulette, during two of the fights the sound stuttering problem returned. That was the only problems all day.

So in Summary, in my experience I CAN still have the problem with DX9, but it is far better and at least playable compared to with DX11.