Hi C.A.,
And welcome to the Axiom forums!
STOP breaking in your new M60s! Mechanical/acoustical break-in is a myth, and happens in seconds. Psycho-acoustical break-in takes longer--it's your brain and ears adjusting to a new reproducer in your room that's imitating the sound of musical instruments and voices.
About your leaving the CD changer running when you go out, I worry that a CD with much louder maximum recording levels may have come on and driven your modest Onkyo into clipping damaging one or more of the M60s's tweeters or midrange drivers. This happe ned to a friend of mine who was an executive at Mirage; he came home to find his amplifier smoking and his M3s silent for because he'd left a changer going, loud, all day.
Play a jazz or rock CD with pronounced cymbals and percussion and put your ear next to the M60 tweeters and midrange drivers to make sure they are working. You can use the pink noise test signal in your Onkyo instead.
The M60's spatial qualities are really very good, which makes me think there may be a midrange tweeter problem.
I can't speak to your Polks other than to say that over the years of reviewing Polks and hearing them at press intros, the line was very inconsistent. Some models were quite good and others very colored and inaccurate.
As everyone has noted, rooms and setup are very important, but please check the midrange and tweeter drivers. Run them full range, "Large", no subwoofer, and let us know.
Regards,
