The volume will be the same only if the voltage gain for the two amps is the same. However, even if the volume is the same, the two systems will sound different. If the systems are in different rooms this probably won't matter, but then neither would different volumes matter, right? I guess I am not sure what you are asking. I highly doubt the two amps will have the same voltage gain, but the only way to tell for sure is to either know the gain outright, in dB, or to know the amp's voltage sensitivity, i.e. how many volts input to the amp will drive it to full volume. An example could be 2 volts to give 200 wpc. From this figure you can figure out the gain knowing the input voltage and the impedance of your speakers.
