Anything. It literally won't matter a bit.....thank you for figuring that out....for doing the calculations too. I didn't see your entire post. .....and at that preamp voltage level, what rating of resistors would you use?
I think that I will likely try the voltage divider first as my input impedance is so high.
That would be a reason to use the resistances I posted. Exactly.
40nV/√Hz is 5.5µVrms for 20kHz bandwidth, which put through a power amp with x30 gain becomes 170µV which is usually noticable from sensitive tweeters and obvious in headphones, and is significantly more noise than a good power amp will contribute.
And x30 gain amp for sensitive tweeters or headphones would be an awesomely deafening overkill...