I drove the M5s in my 4200 cu ft theatre with my Onk and no sub to enjoyable but certainly not party levels. My Onk was almost as good as Axiom's ADA-1000-2 amplifier. Your Onk is not quite like mine but it will power the M5 in your smallish room as long as you're not looking for a disco fever experience. I'd go ahead with the M5 if I was you. Your Onk will not get destroyed if that's what's worrying you.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated