Since that S&V test says "over 300W" in bridged mode, then it sounds like it would NOT be safe to run the m50's with the 875 bridged... correct?
No it would be safe. The rule of thumb I have always used when matching speakers and amps is to use a minimum amp power of 2X the speakers nominal power handling. That way you avo.d clipping in all but the loudest passages.
Another thing to keep in mind with that receiver is to NOT set the speaker impedance in the menu to 4 ohms as it will limit power output to 55 wpc all channels driven. No reason given for this except I suspect its related to its different design with few capacitors and kept low in order to get certified. That means it will clip more easily. I don't like the amp in that receiver primarily for that reason. Capacitors and how they are arrayed are important determinants to how fast the amp can respond to voltage demands and how much spare power is held in reserve.
