blAstroIf it helps, I have these sound settings and have used them previously on dx8. ((I would recommend these sound settings for competitive TF2 as well)):
dsp_enhance_stereo 0 dsp_slow_cpu 1 snd_async_fullyasync 1 snd_pitchquality 0 snd_spatialize_roundrobin 1 snd_mixahead .05
Try those settings, I hope they work.
EDIT:
Perhaps I should link my DX8 launch options as well...
-novid -mat_dxlevel 81 -noforcemaccel -noforcemparms -noforcemspd -console -windowed -noborder -h 1080 -w 1920
Remove the windowed noborder if you don't like borderless windowed mode, it's all preference.
I'm afraid your sound settings didn't do anything for me, and adding -mat_dxlevel 81 seemed to launch tf2 as expected without any sound glitches, but when I closed and restarted TF2, the game was started with dx9 even though I had that command in the launch options. Using mat_dxlevel 81 in the launch options or as a command seems to give me fucked up audio all the time.