[QUOTE=Robbo]Using the same tweeter doesnt necessarily mean they sound the same - the crossover has a huge part to play too![/QUOTE] I know Robbo, and I understand that, but the crossover frequencies of the 2 speakers are the same as well - leading me to believe that those are the same as well. Again, could be wrong. I am sure the M53 dont sound exactly like the M51, but I'd be willing to bet they are similar - certainly they are if what one of my MSN buddies who has also bought and sold a pair of M53's has said about them to me.... and FWIW he said he noticed big improvements by placing a set of Dynaudio Audience's in their place. I was only trying to help, after all I wouldnt want to see him waste his £5 an hour on something he wouldnt be happy with in the long run, but AFAIC, he can take it or leave it.