30 watts on your amp is the maximum power it can deliver, so when your volume control is at maximum it outputs 30 watts.
I've been avoiding this thread, because speaker wattage ratings are probably the most misleading, bogus, meaningless specifications in all of audio, but out of boredom I read through it. As a start, just saying, the above quotation is completely incorrect.
Power amplifiers work on the principle of fixed gain. In other words, how much a given input voltage is raised to a given output voltage. Because this factor is a big number it is described in decibels, and a typical power amplifier gain specification is 26 to 32 decibels. Another way of saying it is that the output power an amplifier delivers is directly proportional to input voltage provided by the source. In this case, 30 watts is the power limit of an output channel stage, and it could be reached at any volume control position where the input voltage and the amplifier's gain factor results in an output power equal to or greater than 30 watts.
