where can i get a decent hifi system in the uk

my present LG hifi system that i got from argos is not that good, music sounds muffled on it when you turn the volume up, and the speakers can't handle loud volume....i would want a better hifi system with surround sound or at least enhanced/ better sound than this which i've got.

and preferable online, i'd like to purchase the hifi online from a reputable website, does anyone know of anywhere?