Danno, any modern solid-state receiver can drive the M80s; the question is how loudly. Don't be overly impressed with 100 watt power ratings which, although a nice round number, represent just a 1.25dB increase in maximum output level capability over your 504, which is rated at "only" 75 watts. For example, if a brief peak could be played at 110dB using 75 watts, it could be played at 111.25dB using 100 watts, a barely noticeable difference.
Get the M80s if you like and see if your present receiver meets your needs; don't spend money based on a possibly groundless assumption. Try before you buy.
