Mojo - I would more likely pair the M5's with the Lgeacy Signature SE's we have here and see how they fare with an $8000 speaker.
To make things "fair", I would cross both speakers at 60 Hz and use an EP-800 for the deep stuff, as the job would be to find out how well the M5's would compare above 60 Hz.
The Legacies are $7000 per pair and include dual 10 inch subwoofers.
Listening would be done level matched and blind, with instant A/B switching, using our pre-amp level unit.
And even then, there's no guarantee one would be "better". It's just an honest way to compare speakers.