The recommended amplifier power for the 11a is 20 - 550 watts per channel, so your AR D400 is plenty of power and a 15 amp circuit will provide plenty of electricity to your amp, unless you're determined to drive all your neighbors out.
The MLs like power so you're good there. I think you'll hear a big improvement with the 11a over the Aerius.
The 11a drops to an impedance of .6 ohms at 20khz, so ideally your amp would double power output down to 2ohms. But there isn't much music at 20khz and we can't hear it anyway, so if the amp sounds good to you, you're good.
The MLs like power so you're good there. I think you'll hear a big improvement with the 11a over the Aerius.
The 11a drops to an impedance of .6 ohms at 20khz, so ideally your amp would double power output down to 2ohms. But there isn't much music at 20khz and we can't hear it anyway, so if the amp sounds good to you, you're good.