From my experience it will continue to improve its sound. After 400 or so hours it really opens up least my P4600 did. Highs will get smoother with the sound having no grain and the bass will get tighter with the soundstage expanding.
New Accuphase Factory Tour
If you have the time this is a fascinating video of the Accuphase factory. It shows the amazing hand made process and the immensely detailed Quality Control for each unit.
I own a P4600 power Amp and it is a joy to listen to every day. It sounded great out of the box and over several months blossomed with warmth, transparency and openness. It is also a beautiful product to look at. You want to touch it to feel it’s quality materials I consider it a piece of Component Art. As you can tell I’m an Accuphase fan. Best amp and component I’ve ever owned
https://youtu.be/upvfySyKRDs?si=1j0icHF0_E0VcIVm