Every modern amps should have antisaturation circuity, low powes one especialy. With low " normal " listenig level is average output power cca 1 - 5 W ( depend on sensitivity of boxes ), but in music are voltage peaks 15 - 20 dB and so you must to have power 50 - 100 W. If you have lower output power, amp will be overloaded and is very much matter for good sound, how will be his behavior in this case. By mostly of amps ( because they have any antisaturation circuity ) you get in this case " avalanche " of saturations practicaly in all stages, which dramatically makes longer recovery time of amp and it is very good hearable as " harsh " sound. Many people says " 5 W is enough for me, 'cos I am listening silently " , but if they have peak detector, they start to talk quite differently.