Help to replace component in micro-system Yamaha MCR-E600

I bought Yamaha micro-system MCR-E600 a month ago buth unsatisfied with the musical sound. Some frequencies in mid are just to loud, depress other tones. I want to replace the receiver OR the speaker with other component.
My choices are: replace only the receiver with Cambridge Azur 540A or NAD C352CT, OR replace only the speaker with Diamond 9.1. I read those components got best reviews Is anyone can help me which the choices? or any other sugestion to improve my micro system sound?
Thanks