Doesn’t the (hw) device also have low enough latency?
How short are the selections you are trying to play?
By the way it’s Device Toolbar that has the output and input selectors.
If users experience a problem that requires to change this setting, it is almost always a recording problem (at least on our main user platform which is Windows).
The Manual for the next release of Audacity will make very clear that the “Audio to buffer” setting also affects playback.
You don’t say what playback device you are using, but if it’s an external card it may have its own buffer setting.
I think dmix is generally regarded as “old” and with inferior mixing algorithms compared to pulse.
Gale