It is important to understand that the MCA225's output is specified as:
225 W, 8 ohm load, 400 W, 4 ohm load, 20-20,000 Hz, at <1% THD
It is also specified for 100 W, 8 ohm at much lower (say inaudible) distortions: 0.001% 1 kHz, 0.015% 20,000 Hz.
So you can see that it is not fixed at 225 W. In fact, any amplifiers, even if specified 1,000 W or more, will only "deliver" what your speakers would draw. In other words, it is up to you to set the volume level and your speakers to draw the current at that volume setting, and would vary according to the media contents you play.
Your Aria 906 will not be at risk at all as long as you don't turn the volume up to the point you can hear any hints of distortions, and when you do, turn it down. If you don't follow good practice, even a 100 W 8 ohms rated amp can, and will blow your speakers.