Important general point, JLM, but I think the math is a little off. 100 watts is only 10dB louder than 10 watts, and doubling of watts only leads to 3 dB increases in acoustic power output each time. But doubling of perceived volume is a different matter, and is frequency- and dispersion-dependent. On a desktop, none of this should matter much, though. Small amps should do fine with nearly any speaker.