Thinking of buying a new A/V Amp and DVD player. What I dont want is to waste money on incompatible systems; ie where one system will outperform the other. I have heard that there is a general rule when buying sources to go with your Amp and that is that the source should cost roughly twice as much. This apparently is not set in stone but is used as a general buying guide. Can anyone tell if this is true, or if not, can anyone enlighten me?