I had the XA100.5 with my Mini IIs. They are 87dB and 4 ohm load. My room is 15 X 16 X 7.5. The needle only moved rarely meaning that it stayed in Class A for most of the time. However, I switched to the XA160.5 for a more effortless, dynamic sound. Magico speakers are deceiving about how much power they need. The S3 is 88dB and 4 ohms. I think it will depend on your room size, listening volume and music type.
I have always found that more power is better with Magico. The XA100.8 may be different as it has more current, but it also has a different sound and is considerably more expensive than a good used pair of XA100.5s. Is there any way to audition the amps before you buy?