I purchased a used amp & subsequently used it to break in a new pair of VR4 GenIII spkrs, which suggest loud volume for 100 hrs.
During the first two hrs. of max volume, there was an electronic smell coming from the amp I hadn't noticed before & from talking w/my dealer & the amp manufacturer, found out the amp had never been fully broken in.
You don't have to run it wide open all the time to break it in but I would suggest opening it up for a few hrs. to see how it performs, how hot it gets & so on but mainly to see how well it sounds while playing the same music at different levels.