I found the synergy of same brand to be most important with I/C's and speaker cables as they are the most "Intimate" with the signal. I am a big believer in after-market power cords as well but find that since they are delivering their "signature" before the component does its job, then they are less needed to synch with the output of that particular piece...For example, I too am a huge Harmonic Tech fan and have been moving up their line for well over 10 years and currently love the Pro 9's with the Magic 2 I/C's (also their Magic Digital Link between transport and Dac), but after some experimenting with their power cord I have found other [brands] that work better in my system.
Good luck and enjoy,
Good luck and enjoy,