If you like the M3's, there is no reason to buy new speakers...I remember listening to a pair many years ago and they were superb loudspeakers. They are power hogs, 7 ohms nominal with 4 ohm minimum impedance, and 85.5dB sensitivity. The Pioneer will likely drive them to an average listening level, but I would advise the connection of an external power amplifier if concert-hall levels are desired without clipping the internal amplifiers, which can kill your tweeters. The big Mirages will be at their best with a stout power amplifier behind them. The Pioneer's preamp outputs can be used to drive such an amplifier, and its internal amps should suffice for reasonable-level listening while you shop for a good power amplifier. Emotiva and Outlaw have good, clean units at reasonable cost, and if you can install the amps in a closet to dampen fan noise, professional amplifiers from the likes of Crown, QSC, and even Behringer (WmAx loves his EP2500's, he has a gaggle of the units) are an excellent choice.
Good luck, those are some very fine loudspeakers indeed. No reason to ditch them at all, IMHO.