I'd say Honesthoff's estimate is a good,conservative one. As always,if you really want the real numbers,Klaus is 'da man to call. Any Extreme model,whether the Stereo or,especially the Monos,will output all day long at 4 ohms and not even notice it or even go warmer than tepid. Comparable to perhaps a Corvette running at 3000 RPM. My experiance with owning ICE amps is limited to the early Acoustic Realities,but my Stereo Extreme was much more "musical"(which varies from person to person) with 4 ohm speakers. If the Mirage's are truely voiced for switching amps,they may have a synergy that would be hard to beat. If you prefer the most detailed sound above all else,than switching will give you that. I still find something in the upper mids,lower treble for me that's just not quite "right"(although I haven't heard any of the latest ones). YMMV.
Good luck