Regarding the SR Black fuse morphing with break-in, even installed in my REL sub the higher frequencies became harsh for a time and then we went to the "bass all over the place" phase as well.
As a result, I was also moved to put micro fiber towels into the rear ports of my speakers which are, of necessity, rather close to the front wall. Oddly, I was also moved to simultaneously turn my REL down a notch in volume.
Patience during break-in is rewarded by the sound I'm currently experiencing--smooth, liquid, detailed and extended. Might be time to bump the REL up a notch. We'll see. Sounds fantastic right now...