JJ, don't know what "max-9dB" means, but whatever it is, the setting of the volume control on different makes of receivers doesn't indicate their relative power capabilities. If you measure the loudness with an SPL meter, both of those receivers will be able to produce equal loudness levels, but the volume control may be calibrated differently, so one of them(even the more powerful of the two)may require a higher setting for equal loudness. Apparently in your case the Onkyo requires a higher setting for the same power output. The difference between 120 and 130 watts is only about 0.3dB in maximum loudness(e.g., 110dB vs 110.3dB)which is essentially meaningless. At the loud level that you're listening, the receivers aren't using anywhere near their maximum, probably just a few watts on average. The fact that the volume control may be near the maximum doesn't mean that the power output is near the maximum; it depends on how high the level of the source material is at that moment. For example, if someone is whispering the receiver may put out 1 watt or less to reproduce that even if the volume control is all the way up.
No, don't select the 4 ohm setting; that reduces the maximum voltage that the receiver's power supply section can output, and therefore the maximum power capacity is also reduced(as much as 50%).
