Hi Mark T,
I just returned from several days of meetings and a day of listening comparisons at the Axiom plant.
Don't think of a floorstanding speaker as a "substitute" for a subwoofer. ALL speakers need subwoofer assistance, to extend and increase output of the bottom octave of music as well as movie effects.
If you are sitting at the other end of your 20-ft room, you'll experience a somewhat "fuller" sound with the M60s over the M22's (both used with a sub) without giving up any detail or clarity. The dynamic potential will also be greater with the M60s. If you sit closer (as I do, about 10 or 12 feet away) with the M22's, there's no need to get the M60s.
But whichever you choose, don't hold off on the subwoofer.
Axiom Resident Expert