Normally you would want to match cables. If you are concerned about them being the same lenght why wouldn't you be concerned about them being the same cable? It maybe slight but each type of cable has it's own sonic signature by mixing you maybe affecting sound, dynamics, range etc. The bottom line IMHO is if it sounds good don't worry about it.
20 to 25 cm at nearly the speed of light would not make a perceivable difference. Silver is usually preferable for the highs but it's all a matter of taste and component matching. If the system seems bright, try the copper for the highs. The same goes for speaker cables.
You must have a verified phone number and physical address in order to post in the Audiogon Forums. Please return to Audiogon.com and complete this step. If you have any questions please contact Support.