I have a Pioneer SX-316-S stereo. It has six speakers. The specification says it consumes 320 Watts. It also says the continuous power output is 100W per channel. It also says the RMS power output is 144W per channel. When I advertise this thing, how many Watts can I call it? 320 Watts? 600 Watts? 864 Watts?
The specification says it consumes 320 watts.
I would go with that as a first estimate and, assuming that is a Class A-B type, that the efficiency is about 50 to 60% at maximum volume and so the audio output is about 160 W.
It also says the continuous power output is 100 W per channel.
You can't get 600 W out for 320 W in so someone is stretching things. Each amplifier may be capable of 100 W but the PSU won't be.
It also says the RMS power output is 144 W per channel.
RMS isn't applicable to a power measurement. RMS stands for root mean squared and is related to the heating power of a waveform. Since \$ P \propto V^2 \$ or \$ P \propto I^2 \$ the squaring has already been done. Power rating should be quoted as the peak power or the average power for a particular test signal - sinewave or a particular piece of music.
When I advertise this thing, how many watts can I call it? 320 watts? 600 watts? 864 watts?
I would recommend that you say something to the effect, "Fills an 8 m x 5 m room with dance party level music with good bass and without distortion."