Melm, The AC9 typically firms things up, but power cord performance varies in different systems.
There are no absolutes with power cord performance.
200 hours should be enough break in time, so I would wait until you reach that point. I would also turn off the Sim for at least a few hours at the end of the break in, and then turn it back on, let it warm up and see what you hear. If the low end is still absent at that point, I'd return it.