The M3s are much bigger and can therefore play much louder (and cleaner out loud levels) and lower. You could get away with not using a sub with them.

The Audiobytes must be used in conjunction with the included digital amplifier. They are not available separately. They are amazing performers for their size and can play quite loudly. You really do need to use them with a sub, but your Polk sub will work with the digital amp.

If I were in your shoes and had the desk space, I'd go with the M3s.