Hi, Phil.
According to Magic D (and I corroborated this myself with tests in DP 9.52), you can just leave the Dither in the Audio menu always on and forget about it.
It ONLY applies dither when merging, freezing, or processing audio files offline.
It does
not apply when we bounce files via the BTD command, so for bouncing we must do it as usual manually by setting a limiter at the end of the master fader with dither whose bit depth matches whatever you chose in the BTD dialog box (16 or 24 bits),
For exporting audio, I don't remember testing it, so I don't know if it applies there (probably not).
Also, I remember my tests revealed a bug regarding dither
all across DP when working at 24 bits (Dither command in the menu and all DP plugins that offer it). DP ignores the setting and doesn't actually apply it! The resulting file comes out without dither! All other offered bit depths work as expected.
I tested this a few years ago, so IIRC, I merged and froze a test file with dither checked/unchecked, and at 24 bits they nulled completely

. Working at 16 and 32bFP, the difference meter in the null test spat the dither only, as expected.
There's a DP plugin that offers all bit depths (7, 9 bits, etc). Same story here... all depths work except 24 bits. Same for MWLimiter.
We could settle this with finality if someone volunteers to reproduce (or falsify) my results with the same test mentioned above. It can be done quickly...
I'm curious if MOTU finally fixed this in DP 10 or DP 11...