Power direct from the wall, or Power Conditioner?

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The question is how much energy is required for some impulse reproduction. 18kw means 5W per second, that is 0,005W in a ms.
1000 of these impulses per hour means you need 5W...
I think it is not about the power requirement over a long time but about how fast the energy can be delivered.
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Sorry to be pedantic, but a Watt is a measure of power which is the rate at which energy is being delivered/used (Joules per second).  18 kW means that you're delivering or using energy at a rate equivalent to several household ovens, or about eight or ten typical kettles all at once;  this would mean a current draw of 75 Amps from a 240 V mains system.  18 kW definitely doesn't mean "5W per second" or "0.005W in a millisecond" -- those phrases don't mean much unless you're talking about the rate at which a power usage is increasing or decreasing with time.

If I understand correctly, you're arguing is that although the continuous power requirement might be quite low, there may be a transient power requirement of up to 18 kW.  Needless to say this kind of power would have to be drawn only for a very short time to avoid damage to the equipment and/or blown fuses.  It's true in principle that an audio amplifier could draw power in a peaky rather than smooth manner, depending on its power supply design and the signal it's reproducing, but I must say I'm sceptical of this 18 kW figure unless it's come from an amplifier manufacturer or someone who's actually measured it.