Deadmau, welcome. Simply from the standpoint of basic amplification there doesn't appear to be a good reason to replace your 5660. Except in the highly unlikely situation that you're playing the M22s so loudly(and possibly endangering your hearing)that the designed 5660 limits are being exceeded, it's doing the job as well as amplification can.

If you want to spend money on audio equipment at this time a far better enhancement to your enjoyment of music would be adding a pair of surrounds to make the home listening experience a bit more realistic(using a mode such as DPLII).

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Enjoy the music, not the equipment.