I own the LS50s (passives), feed them with 60w per channel and mate them with a sub in a room that is too big for them alone w/out a sub.
It took about two-three weeks for me to break-in the speakers. But they never sounded harsh, boxy or unrefined in any way during the break-in process.
After the break-in, I noticed they opened-up significantly, the sound became more transparent and I could more easily discern the quality of the records. A change in amp is very detectable on these speakers.
Overall, they are very neutral, honest and smooth speakers.
Before these speaker I was a non-believer in break-in, but these are really such speakers that the transformation is very noticeable.
Then I wanted to go u/g to the LS50w. I heard them on High-end audio in Munich, they sounded very nice with vocals, but I noticed the boxyness.
Second time I heard a pair right out of the box with zero break-in and they sounded very muffled and boxy. I decided not to upgrade.