Streamer always on?

Question.

 Do streamers have to break in the way everything else does?

The reason I ask is that it seems to be sounding better after a couple of days.

Break in always helps, as you already noticed, especially if there’s an internal DAC 

FWIW, A wise, very experienced electrical engineer once told me that all electronic gear is designed to run hot. Going from hot to cold & back again is the greatest stress on the gear. Then there's the cost of the electric bill to consider.

Temperature cycling is a common method for testing component reliability and life testing. Most if not all discrete electrical components last longer when temperature cycling is minimized or avoided altogether.