Since the M70 is a 10 cell (15v) box, it really should only be compared against other 10 cell boxes. Likewise, 8 cell boxes should be compared against other 8 cell boxes. A 12V boombox operating at 15V would give higher performance results. In fact, the Sanyo M9994 being only an 8 cell boombox might perform much better in terms of power were it to be powered at 15 volts instead of the normal 12volts, and provided the over-voltage does not damage other components. Most amp modules can operate under a wide voltage range with different outputs depending upon the power input.