My two cents:
Power cord....you must get the RFI/EFI right from the start otherwise noise will affect the chain of components to never return. I use Stage lll with a wonderful affect. Power supplies via manufacturer vary to a great degree so YMMV. Try on your TV to find out noise cancellation. The picture won't lie.
Interconnects.....source to preamp. next preamp. to amp.
Speaker Cable.....all to a varying degree but the least in my experience if the front end is taken care of.
Everything lost in the chain will never return so it all matters.
Gwalt