Updated my streamer so do I now have to burn it in. Denafrips dac required it,

no

It may get a wee bit better after 100 hours but I don't know that it would be a big difference. The best person to ask would be tech support of the manufacturer.

Yep …. No surprise here.

My brand new MOON 280D MiND2 streamer/DAC manual highlights 400hrs as the recommended break-in period, during which audio performance will improve.

Now being about a quarter way through it to date…. Yup …. There is a distinct progressive audio improvement to date, and experienced in steps. It has not been a linear experience, but rather in a ad hoc series of steps.

I leave it on full time at least for now, even when I’m not playing tunes through it.

Doing something like this gives a feeling of satisfaction. A sonic improvement is highly unlikely. 

I felt my Streamer and DAC improved after a few hundred hours use, but regardless, they will break in or not as you use them, so just enjoy and come to your own conclusions in a month or so...it's a petty debate as everything breaks in regardless...

And you don’t need your amp turned on to break in DAC and Streamer…

If you've got new electronic parts, the sound is very likely to change subtly over time. 

I built my own amps from Nelson Pass designs and was able to compare two boards with identical designs, but with higher-quality parts in the new board.  At first I was so disappointed with the new build because I spent so much money, time, and effort on the parts and it actually sounded worse than the original.  Two weeks later it was leaps and bounds better, as I had originally hoped when I undertook the build.  After that experience I'll never doubt the reality of burn-in again. Or parts quality for that matter.