JL,
Hello and WELCOME to the PSA Forum! 
If you haven’'t yet seen, this thread (Stellar Power Plant 3 for a modest system) might answer some of your questions. My P3 has about 150 hrs on it and I believe it is still breaking in. Unfortunately, when received I was still breaking in speaker cables, but today have settled on the Morrow Audio SP4 cables (they now have 500+ hrs on them and sound Superb), thus will be closely monitoring any Additional sonic gains that the P3 could offer my overall music system after 300-400 hrs of break-in! 
Ted