Sorry to ask but, but why would you want to do that, adding white noise?
I have 2 questions,- couldn't you use foobar dither instead? (well I know it can only be used at 16 bit output)- What kind of DAC's would not like (digital) silence?
One possible explanation is that only foobar output is truly all zeros when the signal is silent, but I have no way of proving that right now. Suggestions on how to test this are welcome.
See this topic, maybe.
Should the desired output bit depth influence this decision?
If I wanted to mimic TPDF noise what would I choose?
It depends on what you want.
if I wanted to dither to 16 bit output format , using your plugin , would the usual way be to set the noise to the 16th bit? Similarly if the target format is 24 bit should the noise in your plugin be set to the 24th bit?