What the efficency in db means is that at 1watt with a microphone at one meter from the cone the speaker will output 92db of sound. It does not say anything about the speaker's power handling. With 65 watts, your speaker, with a microphone 1 meter from the cone, will do about 110db on paper. This if figuring that it is done in an anechoic enviroment, which your listening room is not. In your listening room, there could be considerable gains or losses from this number depending upon your room's frequency response characteristics.
Typically, on a high quality receiver, the amplifier will reach maximum clean rms power at 0db, or reference level with two channels driven. This is usually not the case in surround mode, it can be different receiver to receiver. Most Harman Kardon receivers I have seen reviewed usually reach .1% thd around -10db on the volume control, with all channels driven simultaneously. Yours could be different. In 2 channel mode I would think it would go to 0db unclipped.
In response to your last question, yes. You will get more power but with increased distortion, most likely becoming audible. You could risk sending the amlpifier into clipping.
